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B739 / AT75, Medan Indonesia, 2017
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|On 3 August 2017, a Boeing 737-900 landing at Medan was in collision in good daylight visibility with a departing ATR 72-500 also on the runway and both aircraft sustained substantial damage. Significant debris was deposited on the runway but there were no occupant injuries and both aircraft were taxied clear. Although ATC were advised of the debris, the runway was not closed until several minutes later after further use had occurred. The Investigation is continuing but has found that the ATR 72 failed to comply with its clearance and that an incomplete readback went unchallenged by ATC.|
| Actual or Potential
|AGC, HF, RI|
|Flight Conditions||On Ground - Normal Visibility|
|Type of Flight||Public Transport (Passenger)|
|Intended Destination||Medan/Polonia International|
|Type of Flight||Public Transport (Passenger)|
|Location - Airport|
|Tag(s)|| Aircraft-aircraft collision|
Copilot less than 500 hours on Type
|Tag(s)|| Incorrect Readback missed|
|Tag(s)|| Accepted ATC Clearance not followed|
Incursion pre Take off
Incursion after Landing
|Damage or injury||Yes|
|Causal Factor Group(s)|
|Group(s)|| Aircraft Operation|
Air Traffic Management
On 3 August 2017, a Boeing 737-900 (PK-LJZ) being operated by Lion Air on a scheduled domestic passenger flight from Banda Aceh to Medan as JT197 collided in normal day visibility with an ATR 72-500 being operated by Wings Airlines on a scheduled domestic passenger flight from Medan to Meulaboh as IW1252 shortly after it touched down on runway 23 at destination. Both aircraft sustained substantial damage but none of the 223 occupants were injured and both aircraft were taxied clear of the runway. ATC were advised of resultant debris on the runway but allowed the runway to remain in use until other aircraft subsequently using it had also reported the presence of debris, after which it was closed.
An Investigation was initiated by the Indonesian National Transportation Safety Committee (NTSC) - the Komite Nasional Keselamatan Transportasi (KNKT). Data from the FDR and 2 hour CVRs of both aircraft were successfully downloaded and used to support the Investigation. ATC recorded data were also available.
The 45 year-old Captain of the 737, who had been PF at the time of the accident, was recorded by the Investigation as having 2,300 hours total flying experience, all but 4 of which were on type. The 23 year-old First Officer on the 737 was recorded as having 500 hours total flying experience, all of which were on type. The 59 year-old Captain of the ATR72, who had been PF at the time of the accident, was recorded by the Investigation as having 13,600 hours total flying experience of which 624 hours were on type. The 23 year-old First Officer on the ATR 72 was recorded as having 263 hours total flying experience of which 109 hours were on type. A third "observer pilot" was occupying the supernumerary seat in the ATR 72 flight deck.
Three controllers were in position at Medan Aerodrome Control at the time of the collision, a 34 year-old Supervisor employed there since 2014, a 24 year-old TWR controller employed there since 2017 and a 23 year old GND controller employed there since 2016.
The damage to the two aircraft (see the illustrations below) was indicative of the outer left wing of the 737 having cut off the outer right wing of the ATR 72 and part of the detached wing then penetrating the forward right fuselage in the vicinity of the flight deck. It was documented as follows:
737 - Approximately 3.4 metres of the outer left wing leading edge was damaged; approximately 3.4 x 0.4 metres of slat number 1 on this wing was damaged and part of it of approximate size 65 cm × 40 cm was detached.
ATR 72 - approximately 2.8 metres of the outer right wing was detached from the aircraft and damaged. Part of the damaged wing was found to have penetrated the forward right fuselage near the flight deck.
The Investigation has yet to report analysis of the flight recorders or report any findings about the position of the two aircraft at impact but has noted that the runway width is 60 metres (NB: almost as much as the combined wingspan of the two aircraft types involved) and no evidence of any runway excursion has been documented.
It was established that GND had instructed the departing ATR 72 to route from the apron via taxiways 'U', 'T', 'B' and 'C' to the full length holding point for runway 23 on taxiway 'C' (see the aerodrome layout illustration below). Whilst the ATR 72 was still with GND, the 737 had called TWR to report on the ILS LOC for runway 23 and had been cleared to land. Almost immediately after this exchange had been completed, GND transferred the ATR 72 to TWR with the instruction to continue and hold short of runway 23. On checking in with TWR, this instruction was confirmed but then followed by TWR asking if they were ready for an immediate departure to which the response was in the affirmative. TWR then transmitted (just over 50 seconds prior to the subsequent collision) “IW1252, behind traffic Lion on short final landed passing line up behind runway 23 from intersection D additional clearance after departure direct Meulaboh”. The pilot response was incomplete - "after departure direct to Meulaboh IW1252” but this was not challenged by the controller who merely responded with the TWR callsign “Namu Tower” and the ATR 72 “continued the taxi to line up on runway 23" at intersection 'D' - a rapid exit taxiway (RET) for aircraft landing on the opposite (05) direction. The Investigation noted that the conditional line up clearance had been combined with a departure clearance. Straight after this a second aircraft called in turn on the 23 ILS and was instructed to continue and advised of an aircraft to depart ahead, the latter advice being explicitly acknowledged by this second-in-sequence arriving aircraft. Half a minute later, "JT197 touched down on runway 23 and a few seconds later impacted with the IW1252", the outer left wing of the 737 hitting and detaching the outer right wing of the ATR 72 and the tip then cutting into the lower forward fuselage in the vicinity of the flight deck.
A few seconds later, the 737 called TWR to say that there was another aircraft on the runway which the TWR controller acknowledged and the Supervisor then took over the TWR position. After a second attempt to get a response from TWR, the 737 was instructed to clear the runway on taxiway 'G' and call GND. Once on that frequency, the crew twice advised the controller that there was likely to be debris on the runway and was told by the controller after the second call had been made two minutes after the first that "the runway maintenance unit had been informed". The Supervisor working TWR then twice, just over a minute apart, cleared the ATR 72 to take off but its crew responded with a request to return to the apron "to check whether there was any damage to the aircraft". This request was approved with an instruction to exit via taxiway 'E' and then call GND.
Within half a minute of this another departing aircraft called TWR on 'C' holding short of 23 and after coordinating with APP, the Supervisor working TWR cleared this aircraft to take off and it did so. Three minutes later, the arriving aircraft which had been unable to land because the ATR 72 was still on the runway and had made an orbit on finals, called TWR again on final again and was told to continue. After a further minute and a half, the aircraft which had just taken off advised TWR that there had been FOD on the runway which was acknowledged. Almost immediately after this and just over nine minutes after the collision had occurred, TWR cleared the arriving aircraft to land, which it did about three minutes later, after which its crew called TWR to report FOD on the runway. Finally, half an hour after the collision had occurred, the TWR Controller "announced to all aircraft that due to FOD, the runway would be closed for 10 minutes". It was eventually re-opened after 25 minutes.
The disposition of FOD on the runway for the take-off and landing permitted after the collision had occurred has not yet been documented but an indication of it is provided by the Illustration below.
It was noted that the weather conditions at the time of the collision were good and the only relevant feature was that the variable easterly wind may have created a small tailwind component for traffic using runway 23. Although the 737 was carrying out an ILS approach, the lowest cloud over the aerodrome throughout the period was recorded as 1800 feet.
Recorded events immediately following the collision do not make any mention of the airport RFFS being advised of or otherwise aware of it having occurred or attending either the scene or the two aircraft during or after their taxi to the apron after the collision.
The Investigation noted that Safety Action known to have been taken within the few days following the collision and in response to it included the following:
- AirNav Indonesia Medan issued a Circular to all controllers which included instructions to prohibit departures from RET intersections, to avoid the use of conditional clearances containing the phrase 'behind the landing aircraft' and to familiarise themselves with and implement when necessary the procedures for abnormal and emergency situations.
- Wings Airlines issued 'Pilot Notices' which included requiring compliance with existing taxi procedures and a new requirement that departures should "always (whenever possible)" use the full length of the runway and "always (whenever possible) avoid departing from intersections".
Five Safety Recommendations were issued on the basis of the initial findings of the Investigation as follows:
- that AirNav Indonesia should ensure that air traffic controllers comply with the requirements of DGCA AC170-02 and ICAO Doc 9432 if a conditional clearance is used. [04.A-2017-25.1]
- that AirNav Indonesia should ensure that air traffic controllers listen to (all) read-backs in order to ascertain that the clearance or instruction (given) has been correctly acknowledged by the pilot and must take immediate action to correct any discrepancies revealed by the read back. [04.A-2017-25.2]
- that AirNav Indonesia should ensure that its air traffic controllers properly mitigate any hazard on the runway without delay (and specifically do so) prior to the issue of any take-off or landing clearance. [04.A-2017-25.3]
- that Wings Airlines should ensure that all its pilots read back or acknowledge clearances or instructions, including conditional clearances, in such a manner that clearly indicates that they have been understood and will be complied with. [04.O-2016-25.4]
- that Wings Airlines should ensure that all its pilots understand and comply with air traffic controller instructions or clearances and that they must seek clarification when there is any uncertainty in respect of an instruction or clearance. [04.O-2016-25.5]
On 26 April 2016, a further 3 Safety Recommendations were issued as follows:
- that AirNav Indonesia Halim and the Halim Airport Operator should inform aircraft operators to initiate take-off from the displaced threshold of runway 24. [04.B-2016-57.1]
- that the Directorate General of Civil Aviation should review a requirement for all aircraft movement on the manoeuvring area including the movement of aircraft under tow to communicate with the air traffic controller on the same frequency. [04.R-2016-55.1]
- that the Directorate General of Civil Aviation should develop a procedure for vehicles and aircraft on the manoeuvring area which requires them to be equipped with serviceable lights visible to the air traffic controller. [04.A-2016-56.1]
The Preliminary Report on which this summary is based was published on 5 September 2017. The Investigation is continuing.
- Runway Incursion
- Conditional Clearance Runway Incursions
- Visual Scanning Technique
- Controller Detection of Manoeuvring Area Conflicts
- Cross-checking Process
- Crew Resource Management
- Guidelines for Dealing with Unusual/Emergency Situations in ATC
- Foreign Object Debris (FOD)
- Foreign Object Debris and Damage Prevention
- Post-Incident Airport Operations