Description

On 25 December 2016, an ATR 72-600 (PK-WGW) being operated by Wings Abadi Airlines on a scheduled domestic passenger flight from Bandung to Semarang as WON1986 failed to make a normal touchdown after a stabilised approach in night VMC at destination and, after a rapid succession of five bounces, eventually stopped in a significantly damaged condition but with no injury to the 72 occupants.

The aircraft where it stopped at the extreme edge of the paved surface. [Reproduced from the Official Report]

Investigation

An Investigation was carried out by the Indonesian National Transportation Safety Committee (NTSC) - the Komite Nasional Keselamatan Transportasi (KNKT). Relevant data was downloaded from both the CVR and FDR as were recorded ATC communications and data from CCTV FOD detection cameras along both sides of the runway.  

It was found that the 28 year-old Captain, a British national who had been acting as PF for the flight, had a total of 4,065 hours flying experience of which all but 260 hours were on type. The 24 year-old First Officer was an Indonesian national who had a total of 3,300 hours flying experience of which all but 100 hours were on type.  

What Happened

In slight rain with a light southerly breeze and partial cloud cover with a base of 1,500 feet aal, an uneventful stabilised approach was made to the 2,560 metre-long runway. However, the following landing commenced with a bounced nose gear first touchdown at an 880 fpm rate of descent which was then followed by four more bounces over the next 11 seconds. The third bounce recorded a 6g vertical acceleration and occurred with a 13° roll to the right which resulted in the initial runway contact being only with the right main gear upon which that gear assembly collapsed. Only at this point did the crew appear to consider a go around but this was no longer an option despite a subsequent increase to the power which this would have required. After the final two bounces, the gear collapse led to the aircraft drifting to the right of the centreline before coming to a stop half a minute later with the right main gear still just on the runway - see the illustration below.  The TWR controller had already recognised that the landing had been abnormal and alerted the airport RFFS and once the aircraft had stopped, when the crew also asked directly for such assistance, they were advised it was on the way and to wait for it to arrive. 

The damaged right main gear and propeller. [Reproduced from the Official Report]

Whilst waiting for the RFFS to arrive, the Captain decided to keep the engines running “to provide lighting in the cabin” but when the RFFS arrived at the aircraft a couple of minutes later, ATC instructed the crew to shutdown the engines so that the passenger evacuation could begin. This evacuation was completed approximately ten minutes after the aircraft had stopped.

In addition to the right main landing gear which was folded inward, the right propeller blade tips had been broken off at about 26 cm from the tip and several dents and punctures were evident on the right fuselage. Superficial marking of the runway surface by white paint marks from aircraft fuselage were also found. The passage of the aircraft along the runway is shown on the illustration below.

Why It Happened

Analysis of the considerable evidence found that the initial touchdown had been not only bounced but also nose gear first. Significantly, it also showed that although the generic aircraft type guidance was to begin the flare to land at the 20 feet agl automated callout, this had not happened and the pre-touchdown -2° pitch attitude had been maintained until the first bounce at 2.8 g occurred. The recorded rate of descent at this first touchdown was also found to have exceeded the structural design specification which was itself based on a normal wings level touchdown and it was considered that although no immediate damage had occurred, this first touchdown may well have “degraded the landing gear strength”.

Whilst the impact of the second touchdown was relatively benign, it was also followed by the highest bounce (to 14 feet agl) after which the third touchdown caused sufficient asymmetric main landing gear damage to preclude both a go around and normal directional control. It was noted that in the event of such a high bounce, the Operator’s FCOM mandated the immediate commencement of a go-around by setting an appropriate pitch attitude and power but “the FDR did not record any pilot attempt to go around” with inevitable consequences thereafter.

The aircraft ground track from short final to final stop. [Reproduced from the Official Report] 

Given the PF's familiarity with the aircraft type and the undemanding nature of the approach, the runway and the prevailing weather conditions, the Investigation considered that a potential explanation for the failure to flare may have been the combination of the low intensity runway lighting and the wet runway surface which would have reflected very little light. This could have “affected the pilot depth perception and caused the pilot to perceive incorrectly that the aircraft was higher than the real condition”. However, such an illusion would have had to be powerful enough to cause an affected pilot to completely ignore the sequence of automatic height callouts every 10 feet below 50 feet.

Separate from the immediate cause of the accident, the Captain’s response to the evacuation of occupants once the aircraft had stopped was considered to have been inappropriate in a number of respects including:

• His failure to follow the OM procedure for communication with the both the cabin crew and the passengers.
• His failure to promptly shut down the engines because he appeared unaware that sufficient cabin lighting to facilitate an emergency evacuation at night could be obtained from the aircraft battery by selecting the ‘MIN CAB LIGHT’ switch to ‘on’, a facility which was clearly described in the ‘Emergency Evacuation on Ground’ Checklist.
• Given that the OM envisaged the possibility that the cabin crew might decide that they should initiate an evacuation in the absence of an instruction to do so from the flight crew, it was evident that “the propeller hazard during evacuation was not considered”.  

Two Safety Recommendations were made early in the Investigation as follows:

• that Wings Abadi Airlines review bounce recovery training for all pilots. [04-2016-43.01]
• that Wings Abadi Airlines review emergency evacuation training including joint training of flight crew and cabin crew. [04-2016-43.02]

Safety Action was taken by the Operator in response to these Recommendations as follows: 

• On 10 January 2017,  a ‘Notice to Instructor Pilots’ was issued to “encourage” all simulator instructors to conduct additional training of the Bounced Landing Technique during pilot recurrent training sessions and to review the Bounced Landing Technique during pilot Line Training.
• Emergency Evacuation Training was reviewed and joint emergency evacuation training between pilots and cabin crew was introduced.

The Final Report of the Investigation was approved for publication in January 2019 and subsequently released. No further Safety Recommendations were made.

Related Articles

• Hard Landing
• Flare
• Emergency Evacuation
• Landing Gear
• Go Around
• Pilot Perception
• Visual Illusion