E135, George South Africa, 2009
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|On 7 December 2009, an South African Airlink Embraer 135 overran the recently refurbished wet landing runway at George after braking was ineffective and exited the aerodrome perimeter to end up on a public road. There was no fire and all occupants were able to evacuate the aircraft. The subsequent investigation attributed the overrun principally to inadequate wet runway friction following the surface maintenance activities and noted various significant non-compliances with ICAO Annex 14.|
|Actual or Potential
|Human Factors, Runway Excursion|
|Flight Conditions||On Ground - Normal Visibility|
|Type of Flight||Public Transport (Passenger)|
|Origin||Cape Town International Airport|
|Actual Destination||George Airport|
|Take off Commenced||Yes|
|Location - Airport|
|Tag(s)||Approach not stabilised,|
Ineffective Regulatory Oversight,
Inadequate Airport Procedures
|Tag(s)||Inappropriate crew response - skills deficiency,|
Procedural non compliance
|Tag(s)||Overrun on Landing,|
Collision Avoidance Action,
Thrust Reversers not fitted
|Damage or injury||Yes|
|Aircraft damage||Hull loss|
|Causal Factor Group(s)|
On 7 December 2009, an Embraer 135 being operated by South African Airlink on a scheduled domestic passenger flight from Cape Town to George was unable to stop on the wet runway at destination after touchdown in normal day visibility and overran beyond the aerodrome perimeter before coming to rest on public road. The aircraft was substantially damaged but there was no fire and all 34 occupants were able to evacuate the aircraft, 10 with minor injuries.
An Investigation was carried out by the AAID of the South Africa CAA. The DFDR and 30 minute Cockpit Voice Recorder (CVR) were recovered and successfully replayed. The BCU NVM was also downloaded and reviewed. During the course of the Investigation, two Interim Reports were published, on 22 December 2009 and on 8 May 2010.
It was noted that the aircraft had made an Instrument Landing System (ILS) approach to runway 11 at George with the aircraft commander as PF. Aspects of the approach had not met stabilised approach criteria but at 500 ft aal, the airspeed was in the vicinity of Reference Speed (Vref), thrust was normal and land flap 45º was in transit. Thereafter, speed increased to reach 143 KIAS when passing over the landing threshold compared to the applicable Vref of 129 KIAS and initial touchdown on the 2000 metre slightly up-sloping runway was made with a slight bounce at a speed of 132 KIAS followed by a slight bounce at the latter end of the TDZ after which the ground spoilers automatically deployed.
Braking action was ineffective with the anti skid units acting. As the end of the runway approached, the PF realised that the aircraft was not going to stop on the paved surface and steered it to the right to avoid colliding with the ILS localiser antenna structure sited on a concrete base 163 metres beyond the 60 metres paved stopway which followed the end of the runway. Once clear of this significant obstruction, he had steered the aircraft back to the extended runway centreline, colliding with the approach lights for runway 29 while doing so. He had then attempted to ground loop the aircraft to avoid colliding with the perimeter fence, but this was unsuccessful and the aeroplane continued straight ahead before crashing through it and coming to rest on the adjacent public road just beyond. It was found that the aircraft had left the runway at a speed of slightly over 50 KIAS and had then travelled for a distance of 278metres until reaching the fence. Towards the end of the runway, the Parking/Emergency Brake had been applied to no useful effect by the PNF although they did not recollect this action, which is contrary to Operations Manual procedures unless normal brake system failure occurs.
The final stopping position is as shown on the diagram below taken from the Official Report.
Following the accident, a Notice To Airmen was issued restricting the use of the runway at George when wet. On 26 May 2010, 1800 m of the runway length, excluding only 100 m at each threshold, was resurfaced with a “20mm thick ultra-thin friction course (UTFC)”. Following this intervention, the NOTAM was cancelled.
It was noted that from 16 July to 6 November 2009, the runway and taxiways at George Airport had been subjected to a rehabilitation process to correct poor surface condition and had been intended to maintain the integrity of the pavement for the following five to six years. The work carried out was essentially a short-term holding action and had involved crack sealing and the application of ‘fog spray’ sealant. The Investigation reviewed all aspects of this work and its effects on runway surface friction in depth and found a range of non compliances with the provisions of ICAO Annex 14
In respect of landings on slippery runways, it was noted that the South African Airlink Operations Manual “offered advice for operation on slippery runways, but did not specify how flight crews should make performance decisions on wet runways that “may be slippery when wet”. The table in the manual required knowledge of braking action before slippery runway calculations could be made”.
In respect of the provision of a Runway End Safety Area, it was noted that as George was a licensed aerodrome, and the runway dimensions met the requirements of a code number 4 aerodrome, ICAO Annex 14 prescribed as RESA at least 90 metres long should be present beyond the end of each runway. However, it was found that the AIP Aerodrome Chart for George did not show a RESA at the time of the accident. It was further noted that:
“the distance from the end of the runway to the perimeter fence was approximately 278 m and the terrain sloped down towards the road at a 5° angle. The fact that the pilot managed to avoid the ILS localiser antenna 223 m beyond the runway end (163 m past the stop-way end) limited the damage to the aircraft and the injuries to its occupants, which could have been much worse. Had a RESA been constructed for runway 11 in accordance with the ICAO requirements, an obstacle-free overrun area, free of hazardous ruts, depressions, and other surface variations, would have extended almost to the perimeter fence.”
The Probable Cause of the accident was determined as:
“The crew were unable to decelerate the aircraft to a safe stop due to ineffective braking of the aircraft on a wet runway surface, resulting in an overrun.”
The following Contributory Factors were also identified:
- The aircraft crossed the runway threshold at 50 ft AGL at 143 KIAS, which was 15 knots above the calculated Vref speed.
- Although the aircraft initially touched down within the touchdown zone the transition back into air mode of 1.5 seconds followed by a 4 second delay in applying the brakes after the aircraft remained in permanent ground mode should be considered as a significant contributory factor to this accident as it was imperative to decelerate the aircraft as soon as possible.
- Two of the four main tyres displayed limited to no tyre tread. This was considered to have degraded the displacement of water from the tyre footprint, which had a significant effect on the braking effectiveness of the aircraft during the landing rollout on the wet runway surface.
- Non-compliance with ICAO Standard 2.9.5 of ICAO Annex 14, volume I, Aerodromes: “Information that a runway or portion thereof may be slippery when wet shall be made available.”
- Non-compliance with ICAO Standard 2.9.6 of ICAO Annex 14, volume I, Aerodromes: “A runway or portion thereof shall be determined as being slippery when wet when the measurements specified in 10.2.3 show that the runway surface friction characteristics as measured by a continuous friction measuring device are below the minimum friction level specified by the State.”
- Although ICAO Standard 10.2.3 of ICAO Annex 14, volume I, Aerodromes: “Measurements of friction characteristics of a runway surface shall be made periodically with a continuous friction measuring device using self-wetting features” were met, no corrective action in the form of NOTAM was issued (in a timely manner) to ensure aircraft safety was not jeopardised as called for in ICAO Annex 14 even though the test data was available.
- Non-compliance with ICAO Standard 10.2.4 of ICAO Annex 14, volume I, Aerodromes: “Corrective maintenance action shall be taken when the friction characteristics for either the entire runway or a portion thereof are below a minimum friction level specified by the State.”
- There were inadequate procedures within the regulating authority to prioritise and analyse the results of the runway friction test conducted 30 days prior to the accident in question by an external service provider.
- A significant contributory factor to this accident was the failure by the appropriate role-players to take immediate remedial action following the 6 November 2009 CFME test results [these were the tests carried out on completion of the runway rehabilitation work]. These results were found to be below the minimum friction.
Safety Recommendations were issued both during and on completion of the Investigation. During the Investigation, it rapidly became clear that one of the factors involved was the condition of the runway surface. This resulted in the issue of three Interim Safety Recommendations as follows:
- that the Commissioner for Civil Aviation (CCA) issue a NOTAM restricting the use of runway 11/29 at FAGG by large transport aircraft (> 5 700 kg) when the runway is wet
- that the Commissioner for Civil Aviation (CCA) ensure that the recommended NOTAM remains in force until such time as adequate friction/texture treatment, such as grooving, has been implemented over the entire runway length and width
- that the Commissioner for Civil Aviation (CCA) requires that the ACSA [the Airports Company of South Africa] conducts a risk assessment on the lack of a RESA on runway 29 at George and if found necessary, incorporates some form of arresting mechanism.
Eighteen additional Safety Recommendations were included in the Final Report as follows:
- that the Director of Civil Aviation require the Air Safety Infrastructure Division to establish its own runway friction test division, or establish an independent agency that would acquire its own runway friction test apparatus that meets ICAO doc 9137 requirements. This should be done to ensure that independent friction tests are conducted regularly at all licensed aerodromes to ensure compliance.
- that the Director of Civil Aviation requires the regulating authority, in collaboration with Part 121 operators, conduct a feasibility study into adding hydroplaning to the simulator curriculum were technical capacity exist to do so. It should be borne in mind that the simulator curriculum in force has been scientifically developed and that adding hydroplaning as a discipline should not jeopardise training in critical emergency conditions that could affect the safety of the flight.
- that the Director of Civil Aviation requires that the Air Traffic Services Division of the SACAA should correct, without delay, the errors described below on the George aerodrome chart as published on the SACAA website and in the AIP:
- (i) The runway slope on the chart reflects the values + 0.04% or - 0.04% SLOPE, depending on what runway direction is applicable or considered. The values should be amended to read + 0.4 % or - 0.4%. The values should be corrected on two places on the chart, alongside the runway display and in the SLOPE column at the bottom of the chart.
- (ii) On the left-hand, lower side of the chart, the latitude value is given as 35° 00’ S. This position was found to be an error and should read 34° 01’ 00” S.
- that the Director of Civil Aviation requires that Part 139 of the Civil Aviation Regulations of 1997 and its associated SA-CATS-AH document is revised to ensure compliance with the provisions and international best practices as contained in ICAO Annex 14, volume I and associated documents.
- that the Director of Civil Aviation requires that the Air Safety Infrastructure Division must amend the regulatory requirements to ensure that all reference code number 3 and 4 runways have a 300 m RESA or a means of stopping aircraft that provides an equivalent level of safety as called for in ICAO Annex 14, paragraphs 3.5.1 and 3.5.2.
- that the Director of Civil Aviation requires that the Air Safety Infrastructure Division be strengthened to ensure that adequate skills and knowledge are available to ensure that there is comprehensive safety oversight of the certification of aerodromes and the maintenance of certification standards. This could include the establishment of an office that deals primarily with runway safety. Ultimately, this office should be responsible for all runway safety initiatives.
- that the Director of Civil Aviation requires that clear guidance material is drafted for the aviation industry on the use of fog-spray and seals on licensed runways in South Africa.
- that the Director of Civil Aviation requires that the Air Safety Infrastructure Division should compile a detailed checklist of the civil infrastructure for aerodrome audit inspections.
- that the Director of Civil Aviation requires that the certifying authorities consider, following a feasibility study, amending the landing safety margin of 1.917 (1.92) during wet weather operations for aircraft above 5 700 kg not equipped with thrust reversers.
- that the Director of Civil Aviation requires that the Air Safety Infrastructure Division should, in compliance with the recommendations of ICAO Annex 14, volume 1, attachment A (guidance material supplementary to Annex 14, volume 1) section 7: Determination of friction characteristics of wet paved runways, define the minimum friction levels and publish it in the AIP as a minimum standard. This guidance material should be complied by the SACAA and be made available to all stakeholders.
- that the Director of Civil Aviation requires that the Air Safety Infrastructure Division should, in compliance with the recommendations of ICAO Annex 14, volume 1, chapter 2: Water on a runway, develop guidance material that should be made available to all industry stakeholders. It is essential that the State provide clear guidelines on the inspection of wet runways.
- that the Director of Civil Aviation requires that the Air Safety Infrastructure Division should, in compliance with the recommendations of ICAO Annex 14, volume 1, attachment A, section 8, list the constant friction-measuring devices that are approved by the SACAA and set out the limitations of these.
- that South African Airlink should place the emergency evacuation placard in the form of a placard on the ceiling of the cockpit, allowing for quick access should the situation require.
- that South African Airlink should implement a procedure in the operations manual (SOPs) whereby cockpit crew are encouraged to request the water depth on the runway from ATC during wet weather operations.
- that South African Airlink should consider retro-fitting thrust-reverser systems on their fleet of Embraer 135 aircraft.
- that South African Airlink consider revising its operations manual - aircraft SOPs, as it lacks significant information. It does not designate who is to deal with certain important inspections and tasks, and fails to provide flight crew with clear guidelines on when a go-around should be performed.
- that South African Airlink consider revising its technical log sheet to accommodate a signature, date, time-stamp and comment column, to filled in and signed off after each transit check (external safety inspection) is performed by a crew member and/or maintenance engineer.
- that South African Airlink encourage flying crew to perform go-arounds whenever there is any doubt that the approach and subsequent landing might jeopardise the safe operation of the flight. Detailed statistics should be kept of all go-around’s to ensure that flying crew does not become complacent in their assessment and execution of the approach and subsequent landing.
The Final Report of the Investigation was published in August 2012.
- Runway Excursion
- Landing on Contaminated Runways
- Runway Surface Friction
- Runway End Safety Area
- Background to fog-spray/seal Source: Final Report
- Effect of hydroplaning Source: Final Report
- An Investigation of the Influence of Aircraft Tire-Tread Wear on Wet-Runway Braking, T. Leland and G. Taylor, NASA, 1965