On 16 October 2013, the crew of an ATR72-600 (RDPL-34233) being operated by Lao Airlines on a scheduled passenger flight (301) from Vientiane to Pakse and making a go around in day Instrument Meteorological Conditions (IMC) following an unsuccessful non-precision approach at their destination tracked the procedure as prescribed but failed to also climb in accordance with it and the aircraft crashed into a river killing all 49 occupants.
An Investigation was carried out by an Aircraft Accident Investigation Committee in accordance with ICAO Annex 13 principles. In addition to the usual representatives, the AAIB Singapore assisted in the recovery of the Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR) from the river into which the aircraft crashed. The data from both was subsequently downloaded successfully.
It was established that the 57 year old aircraft commander was an experienced ATR72-500/600 pilot; the 22 year old First Officer had recently obtained a professional pilot licence and a type rating on the ATR72 500/600. An VOR/DME approach was made to runway 15 in accordance with clearance given by TWR ATC.
A thunderstorm was reported to have been approaching Pakse airport from the southwest and "the sound of heavy rain striking the aeroplane could be heard on the CVR".
The Investigation concluded that after failing to complete the approach to a point where it was possible to continue by visual reference, the crew had commenced the lateral track of the prescribed missed approach procedure in IMC. However, having left the decision altitude which had been selected for the approach as the selected altitude rather than setting the missed approach stop altitude of 3500 feet Altimeter Pressure Settings, the aircraft was not put into a climb. Instead, FDR data showed that it had initially tracked level during the required right turn (although a slightly excessive angle of bank was reached) before descending slowly to a minimum of 60 feet agl before a sudden pitch up which "led to a high pitch attitude of 33°" had been made following "a series of Terrain Avoidance and Warning System (TAWS) Warnings". This extreme pitch attitude led to the automatic disappearance of the FD bars. A maximum altitude of 1750 feet QNH was reached before "a push on the control column was recorded and the pitch value significantly decreased". It was stated that the FD bars re-appeared (still) showing a 'fly down' command and the aircraft subsequently crashed with the engines still at climb power.
The Investigation determined that the Probable Cause of the accident was "the sudden change of weather condition and the flight crew's failure to properly execute the published instrument approach, including the published missed approach procedure, which resulted in the aircraft impacting the terrain".
It was additionally determined that the following may have been Contributory Factors:
- The flight crew's decision to continue the approach below the published minima
- The flight crew's selection of an altitude in the ALT SEL window (which was) below the (approach) minima, which led to misleading FD horizontal bar readings during the go-around
- Possible Somatogravic illusions suffered by the PF
- The automatic reappearance of the FD crossbars consistent with the operating logic of the aeroplane systems, but inappropriate for the go-around
- The inadequate monitoring of primary flight parameters during the go-around, which may have been worsened by the PM's attention (being wholly focused) on the management of the aircraft flap configuration
- The flight crew's limited coordination that led to a mismatch of action plans between the PF and the PM during the final approach
A total of 8 Safety Recommendations were made as a result of the Investigation as follows:
- that Lao Airlines ensure that its flight crew are competent in operating the conventional ATR-72 aircraft and glass cockpit ATR-72 aircraft after relevant training (noting that) one of the objectives of the transition course from the basic ATR72 to the ATR72-600 is to give pilots new references and to allow them to re-work their visual scan and the callouts linked to awareness of automated modes
- that Lao Airlines review its reporting system for its flight crew to report operations related issues such as (the) error in the JEPPESEN chart or in other charts to be used in future
- that Lao Airlines include the effects of somatogravic illusions in its flight crew training
- that Lao Airlines ensure its flight crew communicate through headset during the critical phases of flight
- that the Lao Department of Civil Aviation reinforce the oversight of the airline particularly regarding flight crew training related to non-precision approaches
- that the Lao Department of Civil Aviation reinforce the oversight of the operator to ensure that the flight crew are competent in handling the conventional and glass cockpit ATR-72 aircraft after relevant training
- that the Lao Department of Civil Aviation ensure that the operator implements (a) flight data monitoring system
- that the Lao Department of Civil Aviation review its regulation to require all flight crew to communicate through headset during critical phases of flight.
A summary of the Final Report was published in English translation on 28 November 2014 but the full report has not been so published.
The summary English translation published by the Lao Government did not include a copy of the instrument approach chart used by the crew but this is reproduced below. Note that the chart error referred to above is evident. The summary translation available also does not state which pilot was acting as PF or include the relevant Meteorological Terminal Air Report (METAR) and TAF information available to the crew and does not elaborate on the 'series of EGPWS warnings" which occurred or discuss the extent to which the AP was in use.
Instrument approach chart VLPS/PKZ