On 16 January 2017, a Boeing 747-400F (TC-MCL) being operated for Turkish Airlines by ACT Airlines as TK 9491, an international cargo flight from Hong Kong to Istanbul Ataturk via a planned transit stop at Bishkek, failed to land off a night ILS Cat 2 approach at Bishkek conducted in IMC and crashed and caught fire just beyond the end of the intended landing runway. The aircraft was completely destroyed by impact forces and a post crash fire and its four occupants were killed along with 35 local residents with 36 others on the ground seriously injured.
An Investigation was carried out by the Air Accident Investigation Commission of the Interstate Aviation Committee (MAK). Both the DFDR and the CVR were recovered from the wreckage and their data were successfully downloaded. Most of the recorded exchanges between the pilots on the flight deck were in Turkish.
The 58 year-old Captain, who was PF for the accident flight, had accumulated a total of 10,808 total flying hours of which 820 hours were on type obtained under training for and then as commander. It was noted that seven years earlier when he was an Airbus A300 First Officer, he had been involved in a landing accident involving the collapse of the left hand main gear. The 59 year-old First Officer had accumulated 5,894 total flying hours of which 1,758 hours were on type. Both pilots had formerly been in the Turkish Air Force and both had had three days off in Hong Kong prior to commencing the accident flight. A loadmaster and an Aircraft Technician were also on board.
The flight departed Hong Kong with the crew aware that they were likely to encounter low visibility at Bishkek. Having anticipated this, and also having noted generally similar conditions at the two alternates, Astana and Karaganda, a briefing for a low visibility ILS approach to and automatic landing on the 4,204 metre-long, 55 metre-wide runway 26 at Bishkek was conducted. This ILS had a standard 3° glideslope and was Cat 2 capable. The corresponding 100 feet Cat 2 DH, minimum RVR of 350 metres and the runway threshold elevation of 2,055 feet were noted.
Descent from FL340, initially to FL 220, was commenced at 131 nm from Bishkek and after receiving the latest weather, which included RVRs of 400 metres, 325 metres and 400 metres and a vertical visibility of 400 feet. Descent clearance below FL220 was given just 15 minutes prior to the likely landing time as a result of mountainous terrain below. As the aircraft continued towards the procedure initial approach fix (IAF) 16.2 nm from touchdown, the aircraft was still high despite speedbrake deployment and crossed this position at 9,200 feet, well above the specified crossing altitude of FL 060. Shortly after this, the QNH of 1023 hPa was given by ATC and set by the crew and clearance to commence the runway 26 ILS approach was given with descent to the procedure 'platform' of 3400 feet QNH. At 12.5 nm range, the aircraft was at 250 KCAS and the first stage of flap was selected. CVR data showed that by this stage the crew were monitoring altitude and aware that they were still high. Deteriorating RVRs had been passed by ATC during the descent with the one given when the flight was in the vicinity of the IAF being 300 metres in freezing fog, this RVR being below the 350 metre ILS Cat 2 minimum although it had then improved slightly to 400 metres, 350 metres, 400 metres.
Descending through 5700 feet with FLC mode selected and 3400 feet (from which ILS GS descent should then begin at 3.2 nm) as the associated target altitude, the DFDR recorded LOC capture. At this point, there was just less than 3 nm to go to this final descent point. All three APs were engaged in LOC capture followed by gear down and flap 20 with speed continuing to reduce through 190 KCAS. As the 3.2 nm final descent point was reached, the aircraft was still 600 feet above it and only reached and levelling at it with 'ALT HOLD' mode engaged nearly 2 nm further on (see the achieved vertical profile in the illustration below). The ILS GS indication was showing a maximum fly-down deflection and although the GS mode was armed, the GS was not captured. Soon after the aircraft passed over the Outer Marker (approximately 2.1 nm from the threshold) whilst still level at 3400 feet QNH (the charted procedure altitude for this position being 2800 feet QNH), TWR passed the final RVRs as 400/325/160 metres, gave the Vertical Visibility as 160 feet aal and issued a landing clearance.
About 10 seconds after this and with approximately 1.1nm to run to the threshold, the false upper lobe of the glideslope signal was captured and the aircraft automatically initiated descent on it with a vertical speed of up to 1425 fpm. The aircraft began to follow this approximately 9° descent profile at 160 KCAS which took it along the extended and actual runway centreline. The Investigation concluded that once this descent began, the glideslope displays would have been “fluctuating between +/- 4 dots" and noted that 15 seconds after the false glideslope had been captured, 'AP CAUTION' and 'FMS FAULT 2' annunciations had begun. These annunciations were thereafter continuously recorded without any crew response until almost the end of the flight. The Investigation noted that the FAULT 2 annunciation meant that, as the aircraft approached the intended landing runway threshold, the AP/FD system had determined that it could no longer be tracking the ILS GS. This would not only have led to the EICAS 'AP CAUTION' but also to an aural MASTER CAUTION, the removal of the FD command bars from both PFDs and the appearance of a yellow line through the FMA (Flight Mode Annunciator) GS annunciation on both PFDs. In this situation, in common with all other Boeing aircraft types, the AP remains engaged and the aircraft follows an inertial flight path which defaults to a 3° descent profile. This continues until either a valid GS signal is detected, the crew activates TOGA or ground proximity triggers the 'FLARE' mode.
As the aircraft approached the upwind end of the runway, five activations of the EGPWS Mode 5 'GLIDESLOPE' were recorded in a 7 second period and soon after this, the aircraft over flew the upwind runway threshold at about 110 feet agl. The 100 feet agl EGPWS auto callout was followed by the First Officer calling 'Minimums' and the Captain responding that there was no visual reference and announcing a go around. DFDR data indicated that at 58 feet agl, and half a second after 'FLARE' mode had activated, the TOGA switch was pressed and thrust began to increase. Some 3½ seconds later, ground/obstruction impact began 930 metres beyond the end of the runway. Impact at up to 6g led to aircraft break up and a post crash fire which began in the central fuselage area and subsequently consumed most of the structure.
The vertical flight path of the final approach. [Reproduced from the Official Report]
The Cause of the Accident was formally determined by the Investigation as “the lack of control by the crew of the aircraft position in relation to the glideslope during an automatic approach conducted at night in weather conditions suitable for an ICAO CAT II approach and not performing a go-around in due time after a significant deviation from the instrument approach procedure chart which led to a controlled flight impact with terrain (CFIT) at the distance of approximately 930 metres beyond the end of the active runway”.
A total of 12 Contributory Factors were also identified as follows:
- the insufficient pre-flight briefing of the flight crew members for the approach to Bishkek regarding the approach charts, as well as the non-optimal decisions taken by the crew when choosing the aircraft descent parameters, which led to the arrival at the established approach chart reference point at a considerably higher flight altitude (than prescribed).
- the lack of effective crew action to ensure descent required to comply with the approach procedures achieved so that it arrived at the established approach chart reference point at the required altitude despite the flight crew being aware that the actual aircraft position was higher than that required by the applicable chart.
- the lack of the requirements in the Tower controllers' job instructions to monitor for significant aircraft position deviations from the established chart procedures when technical equipment for such monitoring was available.
- the excessive psycho-emotional stress of the flight crew due to the complicated approach conditions (night time, CAT II approach, long working hours) and their failure to correct flight altitude deviations over a long time period. Additionally, the stress level could have been increased due to the crew's (especially the Captain's) highly emotional discussion of the ATC controllers' instructions and actions despite the fact that the ATC controllers' instructions and actions were in compliance with the established operational procedures and charts.
- the lack of monitoring by the flight crew of the crossing established navigational reference points (the glideslope capture point, the LOM and LIM reporting points).
- the flight crew's failure to conduct the standard operational procedure which calls for altitude verification at the FAF/FAP, which is stated in the Flight Crew Operating Manual (FCOM) and the airline's OM (although the Jeppesen Route Manual used by the crew did not show a FAF/FAP on the runway 26 ILS approach chart).
- the onboard systems' "capture" of the 9° false glideslope beam.
- the design features of the Boeing 747-400 aircraft type regarding the continuation of an approach in automatic mode with the constant descent angle of 3° (the inertial path) with a maintained green indication of the armed automatic landing mode regardless of the actual aircraft position in relation to the runway when the aircraft systems had detected that the glideslope signal was missing (after the false glideslope signal "capture") which generated the correct annunciations including aural and visual cautions.
- the absence of a red warning in the case of a "false" glideslope capture and the transition to the inertial mode trajectory which would require immediate intervention on the part of the flight crew.
- the lack of monitoring of the aircraft position in relation to the approach chart by the flight crew, including monitoring by means of the Navigation Display (ND), engaged in ‘MAP’ mode.
- the flight crew's failure to follow the Airline's Standard Operational Procedures (SOPs) regarding the initiation of a go-around in the event of ‘AUTOPILOT’ (which indicates that it is switching to inertial mode) and EGPWS ‘GLIDESLOPE’ Alerts during the automatic CAT II landing at heights below 1000 feet when there was “no visual reference in respect of either the runway environment or with the lighting system)”.
- the delay in initiating a go-around when no visual reference had been established by the applicable decision height (DH) of 99 feet agl with such action only taken at 58 feet agl.
A total of 13 Safety Recommendations have been made at the completion of the Investigation as follows:
- that the Top Management of Aircraft Operators draw the attention of the flight crews to the necessity of flying the procedure detailed on approach charts, of adhering to the criteria for a stabilised approach and landing and of monitoring distance and altitude when crossing reference points (FAF, LOM, LIM) during ILS approaches, especially ICAO CAT II and CAT III approaches. [5.1]
- that the Top Management of Aircraft Operators provide the flight crew training which clarifies that in case of an absence of the required visual reference with the runway environment, a go-around must be initiated no lower than the established decision height/altitude. [5.2]
- that the Top Management of Aircraft Operators conduct additional training on CRM and interaction in the case that one pilot "fears" that an approach (or other stage of flight) cannot be safely continued when the other crew member does not have the same concern as well as providing additional training on the actions required when the "minimums" annunciation is made. [5.3]
- that the Top Management of Aircraft Operators conduct the theoretical and (if required) practical training for flight crews operating aircraft manufactured by the Boeing Company (all models) on the recognition, order and specific features of the conduct of flights of the autopilot switching to inertial mode during the descent on the glideslope (and) to consider the applicability of this recommendation to aircraft manufactured by other companies. [5.4]
- that ATC service personnel, in respect of the pertinent equipment availability, inform flight crews on significant altitude deviations from values established by the approach charts, especially for ICAO CAT II and CAT III approaches and, in case of conditions requiring compliance with Low Visibility Procedures, to consider making the corresponding amendments to the job instructions of air traffic controllers. [5.5]
- that ATC service personnel finish the provision of the Met Report to crews before an aircraft reaches the LIM. The repetitive provision of the already-provided Met Report should be avoided, especially if the flight crew is in the process of conducting an ICAO CAT II or CAT III approach and landing. [5.6]
- that ATC service personnel consider the practicability of an additional requirement in ATC specialists' job instructions to request the flight crew to confirm capturing both the localiser signal and the glideslope signal ("fully established" status) after crossing the FAP for flights conducted in low visibility conditions. [5.7]
- that the Boeing Company and the FAA consider the practicability of improving the algorithm of glideslope capture and of the implementation of a warning in the case of a "false" glideslope capture. [5.8] NOTE: Other certifying authorities and aircraft design companies are invited to consider the applicability of these recommendations taking into account the actually applied algorithms.
- that the Boeing Company and the FAA consider the practicability of changing the autopilot logic in order to prevent occurrences of continuous inertial glideslope descent (in LAND 3 or LAND 2 modes) in cases when the approach path does not enable a landing in the appropriate zone of the runway. [5.9]
- that the Boeing Company consider the practicability of amending the operational documentation (FCOM, FCTM) in order to provide more detailed description of the inertial path flight mode. [5.10]
- that the Boeing Company consider the practicability of amending the operational documentation (FCTM and the B-747 TM) in order to eliminate the discrepancies in the provided actions recommended for the crew in case of "AUTOPILOT CAUTION" annunciation triggering. [5.11]
- that Aviation and the Aerodrome Administrations analyse the acceptability of construction activity in the immediate vicinity of aerodromes and, in case of findings, take appropriate decisions in cooperation with the pertinent authorities. [5.12]
- that the Aviation Administration of the Kyrgyz Republic considers the practicability of amending aeronautical information provision regarding the publishing of a note on the possibility of increasing the safe altitude following an associated instruction from an ATS unit. [5.13]
A Preliminary Report detailing initial progress in the collection of factual information in respect of the Accident and detailing six Interim Safety Recommendations was released on 24 March 2017. The Investigation was completed on 17 February 2020 and the Final Report was then published.