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JU52, en-route, west of Chur Switzerland, 2018

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Summary
On 4 August 2018, a Junkers Ju-52 making a low level sightseeing flight through the Swiss Alps crashed killing all 20 occupants after control was lost when it stalled after encountering unexceptional windshear. The Investigation found that the pilots had created the conditions which led to the stall and then been unable to recover from it and concluded that the accident was a direct consequence of their risky behaviour. It found that such behaviour was common at the operator, that the operator was being managed without any regard to operational risk and that safety regulatory oversight had been systemically deficient.
Event Details
When August 2018
Actual or Potential
Event Type
Human Factors, Loss of Control, Weather
Day/Night Day
Flight Conditions VMC
Flight Details
Aircraft Junkers Junkers Ju 52
Operator Ju-Air
Domicile Switzerland
Type of Flight Public Transport (Passenger)
Origin Locarno Airport
Intended Destination Dübendorf Airport
Take off Commenced Yes
Flight Airborne Yes
Flight Completed No
Flight Phase Manoeuvring
MNV
Location En-Route
Origin Locarno Airport
Destination Dübendorf Airport
Location
Approx. west of Chur
Loading map...


General
Tag(s) Inadequate Airworthiness Procedures,
Inadequate Aircraft Operator Procedures,
Ineffective Regulatory Oversight,
PIC less than 500 hours in Command on Type,
Deficient Pilot Knowledge,
PIC aged 60 or over
HF
Tag(s) Manual Handling,
Procedural non compliance,
Violation
LOC
Tag(s) Flight Management Error,
Aircraft Loading,
Extreme Bank,
Aerodynamic Stall,
Aircraft Flight Path Control Error
WX
Tag(s) Low Level Windshear,
Mountain Wave/Rotor Conditions
Outcome
Damage or injury Yes
Aircraft damage Hull loss
Fatalities Most or all occupants (20)
Causal Factor Group(s)
Group(s) Aircraft Operation
Safety Recommendation(s)
Group(s) Aircraft Operation,
Aircraft Airworthiness
Investigation Type
Type Independent

Description

On 4 August 2018, a 79 year-old Junkers Ju-52 (HB-HOT) being operated by Ju-Air on a non-scheduled VFR commercial passenger flight from Locarno to Dübendorf was taking a sightseeing route in day VMC and was below the highest terrain in its vicinity as it approached the intended exit route from a basin when a loss of control from which recovery was not achieved occurred and the aircraft was destroyed on impact with terrain at 8120 feet amsl, killing all 20 occupants. There was no post crash fire.

Investigation

An extremely comprehensive Investigation into the Accident was carried out by Swiss Transportation Safety Investigation Board (STSB). In the absence of any flight recorders installed in the accident aircraft, establishing the aircraft flight path relied on the assembly and integrated use of eyewitness reports, photographic and video footage shot by both observers on ground and passengers within the aircraft.

This information, in conjunction with GPS and radar position data was used to reconstruct the flight paths of both the accident flight and the one preceding it. In order to determine the positions of the aircraft in space, its attitude relative to the terrain and its speed relative to the ground, “complex photogrammetric evaluations were carried out” especially in respect of the few minutes of flight which culminated in loss of control. To enable this, the valley southwest of the accident site was surveyed using a 3D laser scanner and the resulting measurements incorporated into the 3D terrain model held by the Swiss Federal Office of Topography. A laser scan of one of the other Ju-Air Ju-52s was also taken and the available models were used, in conjunction with the processing of captured image data, to determine the position and attitude of the accident aircraft around the time control was lost.

The acoustic signals from available video sources were also input to spectral analysis in order to produce sonograms representative of the rotational speeds of larger moving parts such as the propellers, pistons, gears and crankshafts. The frequencies and the individual rotational speeds of particular components and the sound signatures were examined to identify any abnormal noise that could be suggestive of a technical defect. This data source was also used to compare reference data containing the characteristic sound signatures of Ju-Air’s Ju 52 aircraft with recordings made during the accident flight both within the aircraft and from the ground with correction for the Doppler effect. It was “generally possible to identify each engine’s crankshaft rate, the blade rate of the propellers, and cylinder rate for all of their nine cylinders”. Since the aircraft had directly-driven fixed-pitch propellers, it was then possible to find the speed of each propeller and its corresponding engine at the known times of the relevant video recordings.

A detailed review of the low level wind velocity which was likely to have existed in the area where control was eventually lost was also carried out in order to help establish how and why the loss of control had occurred and whether a recovery from it had been theoretically possible in the prevailing circumstances. Generally, it was established that the weather conditions within the Locarno-Dübendorf ‘corridor’ on the afternoon in question has been good provided that appropriate attention was paid to the ever present weather-related risks which low level mountain flying in the Swiss Alps could create.

Although numerous irregularities relating to the airworthiness of the aircraft including its engines were found, it was determined that whilst these had represented risks to safe operations generally, they had not been relevant to the specific causes of the accident under investigation. The remainder of the investigation effort was therefore focused on interpreting the assembled flight path evidence and on collecting contextual evidence in respect of the two pilots, the aircraft operator and the oversight of the Ju-Air operation by the State Safety Regulator the Federal Office of Civil Aviation (FOCA).

The Flight Crew

Both pilots were of similar age, in their early sixties and acquainted as friends. They held ATPLs issued by the Swiss authorities which they had obtained on leaving the Swiss Air Force in the 1980s after 5/6 years as fixed wing fast jet pilots with instructor duties. During air force service, the older of the two pilots had been involved in a midair collision during a training exercise after which both pilots successfully ejected from their respective aircraft. He was subsequently found to have been responsible for the collision on the basis of a “lack of caution”. On gaining their civil licences, both pilots had joined Swissair as First Officers flying the DC9-81 and then the Airbus 310 for 14/15 years until promotion to command on the Airbus A320. After 10/12 years as A320 Captain, both transferred to long haul from where they both retired from Swissair three years prior to the accident.

The pilot who had been Captain and PF on the accident flight had obtained his Ju-52 type rating five years prior to the accident and after 176 hours in type was upgraded to Captain. At the time of the accident, he had a total of 20,714 hours flying experience. This included 14,412 hours in command of which 121 hours were on type. During the two months prior to the accident flight, he had made 33 Ju-52 flights, all but 5 of them with the same co-Captain as on the accident flight. The pilot who had been acting as PM on the accident flight had a total of 19,751 hours flying experience. This total included 12,751 hours in command of which 710 hours were on type. During the two months prior to the accident flight, he had made 41 Ju-52 flights, of which 28 had been with the same co-Captain as on the accident flight.

The two pilots were rostered to fly a Ju-Air tour group from Dübendorf to Locarno on the day before the accident and then to bring them back the following day. They agreed that the one who acted as PF on the outbound flight would act as PM on the return one. The flight attendant on both flights was also the tour group leader whilst the group were in the Locarno area. Both pilots had agreed to carry out the two flights on the proviso that Ju-Air would pay for their air transfer to northern Switzerland after the outbound flight and their return to Locarno the following day to operate the return flight.

A couple of days prior to the outbound flight, the accident flight PF had begun some private pilot instructing on a Robin DR400 so he arranged for his trainee to position the Robin to Locarno alone so that it could be used to fly both Ju-52 pilots back to the airfield at Lommis where the Robin was based, which was about half an hour’s drive from Dübendorf.

On the morning of the following day, the Captain who would be acting as PM on the accident flight made three Ju-Air sightseeing flights in command from Dübendorf in another of the company’s Ju-52 aircraft. On all three of these flights, it was found that the aircraft had been flown significantly below 1,000 feet agl in mountainous areas on several occasions and that “the flight crew had disregarded essential principles for safe mountain flying”. In the early afternoon, the accident flight PF flew from Lommis to Dübendorf in the Robin with his trainee where they collected the accident flight PM and flew to Locarno, arriving with plenty of time to prepare for the northbound return flight.

What Happened

The flight departed from Locarno on time with an estimated 3 hours fuel endurance for the planned 1 hour 15 minute flight and, on the basis of excellent visibility and no significant low cloud, a low level scenic route back to Dübendorf was commenced. The illustration below shows the routes of both the previous day’s southbound flight and the northbound accident flight.

Following a westerly takeoff, the aircraft turned left over Lake Maggiore and flew east over Bellinzona before turning onto a generally northerly track. In general, the aircraft proceeded at altitudes below those of the surrounding terrain, which was a routine feature of Ju-Air VFR flights in clear conditions. Contrary to regulations, it subsequently flew over a designated “countryside preservation quiet zone” at a heights of between 400 feet agl and 1,000 feet agl doing so “at times with a minimal lateral separation from terrain”.


The southbound and northbound routes taken by the accident aircraft. [Reproduced from the Official Report]

After crossing the Alps Nadels, the flight continued through the Surselva region at an altitude of approximately 8,200 feet amsl before making a “relatively tight” left turn over Ilanz to resume a generally northerly track past the Crap Sogn Gion mountain and towards the basin southwest of Piz Segnas and the adjacent Segnespass (see the illustration below). Initially, the aircraft approached this basin on the left-hand (western) side of the valley whilst climbing to an altitude of 9,300 feet amsl.

The pilots’ intention was to fly over the Segnespass with a similar limited vertical terrain clearance - 100 feet agl - to that used by the same two pilots when previously making a similar flight.

The final stages of the accident flight path based on radar (blue) and other (red) data. [Reproduced from the Official Report]

The next two Illustrations show respectively the photogrammetrically reconstructed flight path and the ground track of the aircraft as it approached and entered the basin southwest of the Piz Segnas at position F5, where its altitude was approximately 9000 feet amsl, just above the 8,625 feet amsl height of the Segnespass. It then climbed slightly as it flew past the Tschingelhörner mountain peaks on the west side of the basin, when (position F8) engine power was slightly reduced, the aircraft descended just over 250 feet at a rate incompatible with the power reduction alone whilst making a slight right turn so as to pass abeam the Martinsloch.

A photogrammetrically reconstructed flight attitude at sample positions
(the aircraft shown twice its actual size to make it easier to see) [Reproduced from the Official Report]
The ground track as the flight approached and entered and the basin. [Reproduced from the Official Report]

This manoeuvre afforded passengers a view of this unusual hole through the mountain. During this right turn, the angle of attack increased to approximately 15° and then further to 21° as the aircraft began a left turn (between positions F9 and F10) to begin aligning with the intended track across the Segnespass. At this point, the aircraft was flying approximately 410 feet above the elevation of the Segnespass. The view below was taken from the passenger cabin as the aircraft passed position F10 and shows the Martinsloch (red arrow).

A still from a passenger video with the aircraft pitching up 11° but with a 20.6° angle of attack. (Reproduced from the Official Report)

Immediately after the picture above taken at position F10, the aircraft entered a 1200 fpm descent lasting 4 seconds. After position F13, where the left bank had already reached 32.7°, it continued to increase steadily and did not decrease even in response to a significant aileron deflection to the right. The pitch attitude, already negative, continued towards a vertically down trajectory and, approximately a minute after entering the basin, terrain impact occurred at a speed estimated at 108 knots and the aircraft was destroyed and all occupants fatally injured.

Why It Happened

The evidence assembled on flight path and on aircraft control from its maximum altitude of 9,300 feet amsl as it tracked towards the basin southwest of the Piz Segnas intending to exit overhead the Segnespass (8,623 feet amsl) at its head was analysed.

It was noted that approaching the basin at a true airspeed of approximately 97 knots represented an approximate 44% margin above the stalling speed. However, given that some ‘normal’ terrain-induced turbulence had already occurred earlier in the flight and it would be necessary to make a left turn in order to cross the pass, the higher stalling speed in the turn meant that the stall speed margin was inadequate. It was also noted that the lateral and vertical terrain clearances which were both minimal were likely to increase the chances of unfavourable windshear consequences for what was an underpowered aircraft for such low level mountain flying despite the absence of previous Ju-Air accidents due to flight in these circumstances. Taken together, these two factors were assessed as “representing a risky starting point for the continuation of the flight (which) did not then improve”.

As the aircraft was passing the Martinsloch, the initially encountered headwind component “steadily eased”. In this situation, it was concluded that “despite the relatively high density altitude and the poor condition of the engines”, there was still a limited reserve of power when the wind velocity began to change. However, because of the restrictive lateral and vertical terrain clearance accepted by the pilots for this part of the flight any wind-velocity or other difficulties affecting flight path control would mean that there was no alternative other than continuing to proceed over the Segnespass.

It was observed that “one of the basic principles of flying in mountainous areas (is) that there must always be the option of an alternative flight path or to turn back”. It therefore followed that “the flight crew’s decision to dispense with these safety-related requirements created a very high-risk situation which did not permit any tolerance for further errors, faults or external influences” and concluded that “this type of piloting could be seen as a causal factor of the further course of the accident”.

A reconstruction of the flight path and the prevailing wind conditions showed that the brief but rather rapid descent while flying past the Tschingelhörner mountain peaks had been attributable to downdraughts of between 400 and 1000 fpm. An extensive meteorological investigation was carried out and “proved that downdraughts of this kind were present in this area of the basin” and in any case “did not represent an abnormal phenomenon in the mountains”.

At the time of the right turn made in this vicinity, the true airspeed of slightly less than 100 knots and an angle of attack increase to approximately 15° with engine power having been intentionally slightly reduced, the initial response was not to restore power but to increase pitch whilst the descent became increasingly steep. It was considered conceivable that because of preoccupation with the synchronising of the engines after the power reduction and the fact that the view from the flight deck had no obvious reference points would have “made it difficult to easily recognise the descent”, and the inappropriate increase in pitch may have been “made subconsciously”. The fact that the aircraft was operating marginally outside its flight envelope due to a loaded centre of gravity slightly beyond the rear limit could have contributed to the crew response and would in any event have made the aircraft more unstable around its pitch axis, a condition which therefore “represented a factor that directly contributed to the accident”.

Analysis showed that after then entering a significant updraught, the fact that the aircraft quickly transitioned to a rate of descent of 1200 fpm which then continued to increase could not be attributed to a continuing downdraft. Rather, it was the fact that the near-to-stalling angle of attack had existed when the aircraft entered a relatively modest updraft (maximum 600 fpm) which had led to the stall. The vectors associated with a stall condition entered in the circumstances which it was deduced had prevailed was illustrated in the following diagram:


The relative position of vectors when entering an updraught from a downdraught.
Key to the above illustration: Blue - updraught; Yellow - aircraft movement relative to the updraught; Black - aircraft longitudinal axis; Black dashed line - horizontal plane; Green line - chord line; Purple angle - pitch angle; Red angle - flight path angle; Yellow angle - angle of attack. [Reproduced from the Official Report]

It was noted that the flight crew failed to use the available reserves of engine power to consistently achieve the design manoeuvre airspeed “which under the prevailing conditions was a true airspeed of 106 knots”. If, as in this case, the design manoeuvring speed cannot be achieved during horizontal flight, a possibility for an aircraft with a relatively large mass-to-power ratio, it will need to be achieved by descent which in turn requires a sufficiently generous altitude margin to be available, a particularly important, but ignored, consideration in this case. Had more clearance from terrain below been available, the response to the signs that a stall was imminent, which based on their aileron input were apparently recognised, would have been possible. With the prevailing minimal height above terrain and no other escape options, the aircraft was placed in an irrecoverable condition.

The Context for the Pilots’ “Risky Behaviour”

The Investigation examined in depth the circumstances in which it had been possible for the absence of risk awareness in two experienced pilots to develop. These primarily focused on aircraft operator and the oversight of it by the Federal Office of Civil Aviation (FOCA) as Safety Regulator. In both cases, systemic and long standing inadequacies were discovered which it was concluded had created conditions in which an accident like the one under investigation was highly likely to occur at some point in Ju-Air’s operations.

Ju-Air was an integral part of the Association of the Friends of the Swiss Air Force (Verein der Freunde der Schweizerischen Luftwaffe) or VFL to which the FOCA issued all official authorisations and approvals. In the 10 years prior to the accident, its Ju-52 aircraft had carried out around 900 commercial flights each year which carried 13,000 paying passengers. At the time of the accident, the operation was being run by 8 employees supported by 96 volunteers. The latter included 27 pilots and 30 flight attendants who doubled as tour guides on trips such as the accident flight.

The OM was based on that of a conventional airline adapted to a VFR-only operation. However, “a review of numerous flights and planning documents” found that many of its procedures “were merely formal and frequently not implemented by the flight crews during operations”. It was, for example, discovered that it was “common practice to not calculate the mass or centre of gravity, or to do so only partially” and operational flight plans were “generally not filled out correctly and not used in accordance with the requirements”. It was also found that the OM “did not contain any information for flying in the mountains”.

It was also discovered that the series of deficiencies in the way flight operations were conducted included a dysfunctional system of risk assessment with the specific risks of VFR flight or mountain flying never having been assessed. It was also found that despite the existence of an approved Safety Management System, more than 150 safety-related incidents were found in which “the statutory reporting obligation had not been fulfilled and that no in-depth analysis of the events was ever carried out internally”. These incidents were found to include ones in which “the experienced and highly qualified Ju-Air flight crews made mistakes relating to basic flying skills”. It was noted that although the FOCA had “identified these deficits in individual cases, their scope and systematic patterns remained undetected (and) no effective corrective action was requested”.

Since the operator had not had the means to monitor risk in respect of its flights, the Investigation made such an evaluation. This was based on radar data for 216 flights carried out in the five months prior to the accident. Radar tracks were height-corrected for the prevailing pressure and temperature conditions and then analysed paying particularly attention to:

  • Flight phases with no possibility of turning back or alternative flight path;
  • Low-level flights over plateaus at or above 8,200 feet amsl;
  • Approaching and flying over ridges at almost 90° to the ridge and close to the ground;
  • Flight over terrain when significantly below the recommended safety margin or the minimum required flight altitude prescribed for non-commercial VFR flights.

This exercise found that in just over a third of the flights analysed, “elementary principles of safe flight management in mountainous areas were significantly violated” with almost half of these flights involving situations which were considered to have “a very high potential risk”. It was noted that 16 of the operator’s 27 pilots had been initially trained as Air Force pilots and that it was these pilots who were the ones who were mainly “violating elementary safety rules”.

It was concluded that the oversight of Ju-Air by the FOCA in respect of both flight operations and airworthiness had in many respects been ineffective and had failed to provide more than a “limited insight” into what was really going on at Ju-Air. It was considered particularly significant that after one of their very rare inspections of a passenger flight in a mountainous area, the inspector involved “did not fault the flight in any way” despite it being performed:

  • significantly below the required safety margin of 1,000 feet agl on several occasions;
  • the essential principles for safe mountain flying being disregarded;
  • the choice of flight path clearly contradicting the guidelines for flights in the Alps published by the FOCA in the Swiss AIP VFR guide.

This was considered to “exemplify either a lack of critical judgement or a lack of critical attitude on the part of the inspectors towards the flying skills of Ju-Air’s experienced pilots, which led to obvious errors in flight operations not being rectified”.

More broadly, it was found that “the main focus of the FOCA inspections was the formal existence of the procedures specified in the OM” rather than any effective attempt to assess the actual implementation of these procedures. Based on the evidence gathered, it was considered that the FOCA had “acted as if they were unaware of the, at times, serious violations committed by Ju-Air’s flight crews, despite the fact that occasional reports to the FOCA would have given cause for more in-depth investigations”. The consequence of this had been that the FOCA had “not had a true picture of Ju-Air’s operations". It was also noted that “audits of FOCA carried out by the EASA in the years prior to the accident had revealed some of these shortcomings” including “insufficiently in-depth supervisory activities”.

A comprehensive assessment of the available evidence in respect of the accident flight and its wider organisational context resulted in the formal documentation of a total of 14 Safety Deficits. These were as follows and are not listed in any order of significance in relation to the cause of the accident:

  • Inspecting corrosion damage and defects in system components

Considerable corrosion damage was found on the spars, hinges, wing fittings and in the area of the cabin floor panel on the wreckage of the accident aircraft. Two of the three engines were equipped with remanufactured cam discs which exhibited defects. Due to the two other Ju-52 aircraft in Ju-Air’s fleet having the same year of manufacture, type of operation and operating hours, it must be expected that they have similar defects.

  • Laying the foundations for effective, risk-based supervision

Implementation of legal requirements by both the Federal Office of Civil Aviation (FOCA) and Ju-Air for operations with historic aircraft was primarily formal in nature. Many of the processes described in the manuals represented the operational requirements to a limited extent only. In particular, only partial provisions had been made for the relevant risks of VFR operations involving Annex II aircraft, as specified in European Regulation 216/2008 (equivalent to today’s Annex I aircraft, as specified in European Regulation 2018/1139). Overall, the regulation proved to be complex and not well adapted to the actual needs of flight operations. Regardless of the organisational form, the level of safety required for air operations involving passengers should be guaranteed.

  • Issuing exemptions

At the time it was commissioned for use in civil aviation, the accident aircraft was categorised in accordance with legal requirements which had changed over time. As a result, the type classification was no longer correct at the time of the accident. Based on the original classification of the type, various requirements for approval were declared inapplicable by way of exemption. These decisions were not reviewed even in the case of major legislative amendments.

  • Monitoring the operation of historic aircraft

On numerous occasions, Ju-Air’s pilots violated rules and took high risks during the operation of historic aircraft. This high-risk behaviour was not detected by Ju-Air or the FOCA due to a lack of effective management, monitoring and oversight. Numerous other safety-related incidents were also not detected by Ju-Air or the FOCA and, where they had been detected, were not addressed in a manner that enhanced safety.

  • Improving the organisation of supervisory activities

Audits and inspections performed by the FOCA were not capable of providing a realistic overview of the actual operations or actual processes conducted by Ju-Air and in the maintenance companies. Supervision was largely formal and ineffective, particularly as there was a lack of a critical attitude within the FOCA and because the exchange of information between the technical inspectors was inadequate.

  • Improving the level of expertise of the supervisory authority

The staff of the FOCA were often unable to identify the safety-related problems during audits and inspections of Ju-Air and its maintenance organisations. With regard to the supervision of technical aspects, a lack of technical and methodological expertise in such historic aircraft played a major role in this. This led to a certain dependence on the know-how of the staff employed by the maintenance organisations under supervision. With regard to supervision in the field of operations, the inspectors no doubt had the expertise, but acted in a way which was insufficiently critical towards Ju-Air’s pilots. As a result, the activities of these companies were not effectively supervised.

  • Determining performance data for overhauled aircraft

Certain aspects of the accident aircraft’s performance and operating data were no longer accurate or were missing. It was, for example, no longer possible to achieve the documented performance for cruise flight, there was a lack of information on manoeuvring speed, and the performance after an engine failure was insufficiently documented.

  • Reviewing and improving maintenance procedures

Several shortcomings were identified during examination of maintenance work on the Ju-Air JU-52s. This included in particular the documentation for performing major modifications and the management of spare parts. Such deficiencies represent a risk.

  • Retraining flight crews

Ju-Air’s pilots exhibited a tendency towards systemic reckless violation of generally recognised aviation rules. Furthermore, their pilots were found to have insufficient up-to-date knowledge of basic flying principles such as the structure of airspace, flight preparations, calculation of the mass and centre of gravity and knowledge of aviation regulations.

Even with extensive experience, Ju-Air pilots frequently made basic errors such as airspace violations. Despite the fact that the aircraft were often flown by two experienced pilots of Captain rank, these mistakes were not avoided. Performance reviews were occasionally accepted without critical rigour and obvious mistakes were not identified or addressed with regard to corrective action to be taken. Such behaviour is evidence of considerable deficits in collaboration, especially among experienced pilots of equal rank.

  • Improvement of management measures in flight operations

Pilots at the aircraft operator were often irresponsible in the way they dealt with the freedoms provided by the general operational framework conditions. Even experienced pilots who had worked at large airlines for long periods demonstrated this risky form of behaviour and violated basic safety rules. The companies for which they had previously worked all had effective management and monitoring measures in place which would have immediately revealed any deviation from the required quality of work. Ju-Air, in contrast lacked the means and tools to detect these safety issues. It can be concluded that pilots with a long history of safety-conscious environments can become undisciplined if effective management and monitoring measures are not in place.

There were numerous quality issues in respect of the maintenance of the aircraft operated by Ju-Air. Likewise, several examples proved that reports concerning safety-related incidents were not forwarded or processed in a manner that improved safety. This prevented or at least substantially reduced what could have been learnt from such incidents. Although Ju-Air had a formal safety management system in place, it was ineffective to a large extent.

  • Performing incident and risk assessments

Ju-Air never analysed significant risks encountered during flight operations. As a result, operations regularly took place in such a way that a minor malfunction could have caused an accident. The accident under investigation is typical of this, not least because a frequently applied, high-risk procedure coupled with a natural, everyday framework condition had a fatal effect.

  • Improving training for critical flight conditions

Ju-Air’s pilots had no experience of how the Ju-52 behaved in critical flight conditions with a normal passenger load.


The Investigation formally determined that the Direct Cause of the Accident was “the fact that after losing control of the aircraft there was insufficient space to regain control, thus the aircraft collided with the terrain”.


Two Direct Causal Factors leading to the accident were also identified as:

  • The pilots operated the aircraft in a very high-risk manner by navigating it into a narrow valley at low altitude and with no possibility of an alternative flight path.
  • The pilots chose a dangerously low airspeed in regards to the flight path.

It was concluded that both these factors meant that the turbulence which was to be expected in such circumstances was able to lead not only to a short-term stall with loss of control but also to an irretrievable situation.


Two Direct Contributory Factors were identified as:

  • The pilots were accustomed to not complying with recognised rules for safe flight operations and taking high risks.
  • The aircraft involved in the accident was operated with a centre of gravity position that was beyond the rear limit. This situation facilitated the loss of control.

The Systemic Cause of the Accident was determined as: “The requirements for operating the aircraft in commercial air transport operations with regard to the legal basis applicable at the time of the accident were not met”.

Five Systemic Contributory Factors were identified as:

  • Due to Ju-Air’s inadequate working equipment, it was not possible to calculate the accurate mass and centre of gravity of its Ju-52 aircraft.
  • In particular, the Ju-Air pilots who were trained as Air Force pilots seemed to be accustomed to systematically failing to comply with generally recognised aviation rules and to taking high risks when flying the Ju-52 aircraft.
  • Ju-Air failed to identify or prevent both the deficits and risks which occurred during operations and the frequent violation of rules by its flight crews.
  • Numerous incidents, including several serious incidents, were not reported to the competent bodies and authorities. This meant that they were unable to take measures to improve safety.
  • The FOCA failed to some extent to identify the numerous operational shortcomings and risks or to take effective corrective action.

Seven Other Risk Factors which “had no or no demonstrable effect on the occurrence of the accident, but which should nevertheless be eliminated in order to improve aviation safety” were also identified:

  • The accident aircraft was in a poor technical condition.
  • The accident aircraft was no longer able to achieve the originally demonstrated flight performance.
  • The maintenance of Ju-Air’s aircraft was not organised in a manner that was conducive to the objective.
  • The training of Ju-Air pilots with regard to the specific requirements for flight operations and crew resource management was inadequate.
  • Ju-Air pilots had not been familiarised with all critical situations regarding the behaviour of the aircraft type in the event of a stall.
  • The FOCA failed to identify numerous technical shortcomings or to take corrective action.
  • The expertise of the individuals employed by Ju-Air, its maintenance providers and the FOCA was, in parts, insufficient.

Safety Action taken during the course of the Investigation was noted as having included, but not been limited to, the following:

  • Twelve days after the accident, the FOCA issued a number of requirements to the aircraft operator involved:
    • it must equip its aircraft with a logger in order to monitor and evaluate its flight operations.
    • except for during take-off and landing, flight must be made not below 1,000 feet agl above uninhabited areas and 2,000 feet agl above inhabited areas.
    • all passengers must remain in their seats with their seat belts fastened throughout the entire flight.
    • all flight and cabin crew must be given a refresher course on standard operating procedures and crew resource management.
  • On 16 November 2018, the FOCA withdrew the C of A for the aircraft operator’s remaining two Ju-52 aircraft.
  • On 11 April 2019, the aircraft engine maintenance privileges of the organisation responsible for the Ju-Air Ju-52 fleet were withdrawn after an unsatisfactory audit.
  • On 15 October 2019, after Ju-Air continued to carry out aircraft maintenance following the suspension of its authorisation to do so as a result of a series of unsatisfactory audits during the first quarter of 2019, the FOCA imposed a fine.
  • On 24 June 2020, Ju-Air voluntarily returned its suspended Part-145 approval.

A total of eight Safety Recommendations were issued, each corresponding to a specific ‘Safety Deficit’ identified during the Investigation, as follows:

In the Interim Report on the Investigation published on 20 November 2018:

  • that the Federal Office of Civil Aviation (FOCA), in collaboration with the air operator, should take appropriate measures to ensure that (the other two Ju-52 aircraft operated by Ju-Air) are inspected for corrosion damage and defects in system components.
    [No 548]

In the Final Report of the Investigation:

  • that the Federal Office of Civil Aviation (FOCA) should ensure that rules are adapted to air operations with passengers on aircraft referred to in Annex 1 of European Regulation 2018/1139 and that these effectively address the risks specific to such operations.
    [No 561]
  • that the Federal Office of Civil Aviation (FOCA) should, until Safety Recommendation No. 561 has been implemented, ensure that the risks specific to the particular flight operations involving passengers on Annex 1 aircraft, as defined in European Regulation 2018/1139, are identified and effectively reduced with an effort suited to the complexity and scale of the respective operation.
    [No 562]
  • that the Federal Office of Civil Aviation (FOCA) should, when granting exemptions for Annex 1 aircraft, as specified in European Regulation 2018/1139, take into account the risks specific to their relevant operation and periodically review the exemptions.
    [No 563]
  • that the Federal Office of Civil Aviation (FOCA) should, together with organisations which operate historic aircraft primarily for the transport of passengers, define effective risk-based management and supervisory measures which are capable of identifying and correcting the specific problems with this type of operation at an early stage.
    [No 564]
  • that the Federal Office of Civil Aviation (FOCA) should improve its organisation of audits and inspections in such a way as to improve the exchange of information within the authority, as well as to enable both critical analysis of the organisation concerned and the identification of relevant problem areas more effectively.
    [No 565]
  • that the Federal Office of Civil Aviation (FOCA) should acquire the necessary technical and methodological expertise for the supervision of historic aircraft or make it available from an independent party. Furthermore, it should ensure that supervision is exercised in an effective manner. [No 566]
  • that the Federal Office of Civil Aviation (FOCA) should require the air operator (involved) to determine the key performance data of its Ju 52/3m g4e aircraft following a major overhaul, and adapt the corresponding documents accordingly prior to the aircraft type being released to service. [No 567]

It was decided that in view of a number Safety Recommendations already made by other investigation agencies in response to the difficulty in investigating accidents in the absence of crash-protected recorded flight data and the planned changes to aviation law on the obligation to equip aircraft with such recorders, the STSB would refrain from making any further Safety Recommendations to achieve a similar goal.


A total of seven ‘Safety Advice’ statements on specific areas of concern which were also each explicitly identified as ‘Safety Deficits’ during the Investigation were also formally issued as follows:

  • that the Aircraft Operator and its Maintenance Organisations should - together with the continuing airworthiness management organisation (CAMO) - review and improve their existing processes to ensure the traceability of maintenance work and unambiguous spare parts management.
    [No 25]
  • that the Aircraft Operator should provide retraining for its flight crews with specific regard to discipline, compliance with rules and in particular safe flying practices in mountainous areas and the application of the basic principles of flying.
    [No 32]
  • that the Aircraft Operator should optimise collaboration among its flight crews (crew resource management) to meet the specific requirements of its operations (VFR flights, flights in mountainous areas, extensive experience, equal rank, etc.).
    [No 33]
  • that the Aircraft Operator should develop and implement management and monitoring measures to detect and ensure compliance with basic safety principles and legal requirements.
    [No 34]
  • that the Aircraft Operator should improve its internal processes, specifically those in relation to quality assurance and risk management, in order to allow the timely identification and targeted resolution of safety issues.
    [No 35]
  • that the Aircraft Operator should perform the missing incident and risk assessments and ensure that in the event of engine failure and when flying in mountainous areas, appropriate flight planning and route selection will allow for all flights to be completed safely without fail.
    [No 36]
  • that the Aircraft Operator should document critical flight conditions for realistic operational situations and make its pilots as familiar as possible with critical flight conditions.
    [No 37]

The Final Report was approved on 22 December 2020 and subsequently published in English translation and in the definitive German language version on 28 January 2021. It was noted that the Federal Office of Civil Aviation (FOCA) expects that aircraft operations by Ju-Air will remain suspended “for a prolonged period of time”.

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