Description

On 12 March 2018, a Bombardier DHC8-400 (S2-AGU) being operated by US Bangla Airlines on a scheduled international passenger flight from Dhaka, Bangladesh, to Kathmandu as UBG 211 departed the left side of runway 20 at destination following visibly unstabilised manoeuvring in day VMC after a failed attempt to fly a VOR/DME approach. The aircraft continued through the airport inner perimeter fence, caught fire and was destroyed. Forty-seven of the 67 passengers and all four crew members were fatally injured. The remaining 20 passengers survived, all with serious injuries.

Investigation

An Investigation was conducted by an Aircraft Accident Investigation Commission established for that purpose and was conducted in accordance with ICAO Annex 13 principles in accordance with the Civil Aviation (Accident Investigation) Regulation (2016) of Nepal. The CVR and FDR were removed from the wreckage and their data were successfully downloaded. Useful data were also recovered from the Engine Monitoring Unit (EMU) and data from both the EGPWS and airport CCTV were useful in corroborating FDR data.

It was noted that the 52-year-old Captain, who had been PF for the accident flight, had accumulated a total of 5518 flying hours including 2824 hours on all DHC8 variants with 1793 hours on the -400. He had gained his initial pilot experience in the Bangladeshi Air Force which he left after 10 years of service, including as a fast jet pilot, in 1993 after being removed from active duty after a psychiatric examination which confirmed depression. After nine years, he had been assessed at another psychiatric examination and “declared to be fit for flying”. In 2010, he had joined Regent Airways as a First Officer on the DHC8-100/300 before moving to United Airways in 2011 as an ATR72 Captain and later as a Training Captain where he accumulated over 2200 hours in command. He had joined US Bangla Airlines in 2015 as a DHC8-400 Captain and had again become a Training Captain. The 25 year-old First Officer had a total of 390 flying hours including 240 hours on type all gained since she had joined the airline in September 2016 directly after completing pilot training for issue of a CPL at a Dhaka Flight Training School.

What Happened

All the available evidence was used to reconstruct the final half hour of the flight. It was found that although the Captain had made a limited attempt to conduct an approach briefing prior to beginning descent from FL240, this had been “very short” and lacked an adequate briefing on the likely VOR 02 approach procedure for which the Captain did not appear to have his own chart. It was considered that his apparent complacency may have been due to his own relative familiarity with the destination in contrast to his very low experience First Officer for whom this was the first visit. It was noted from the CVR record that during the brief the First Officer had spoken on several occasions in a way that indicated that she “had an incorrect understanding of the procedures to follow during approach and her confusion over the missed approach procedure (which) was never resolved” with the Captain saying that he would “brief the remaining items later”.

Initial descent to FL160 was given together with an Expected Approach Time (EAT) which might involve taking up a brief hold before commencing the approach. On transfer to the APP frequency, further descent clearance to 13,500 feet was given (the aerodrome reference point (ARP) elevation for Kathmandu is 4395 feet) with a clearance limit of waypoint GURAS, the IAF for the 02 approach, to take up the hold there. The IAF was just under 18 nm from the runway threshold and the procedure required the descent from that point to commence at 11,500 feet. The FMS ‘HOLD’ mode was armed accordingly and further descent to 12,500 feet was given at minimum clean speed. A hold of up to 6 minutes appeared likely but then APP gave further descent to 11,500 feet, cancelled the EAT and cleared the flight to commence the approach without any delay with GURAS only 3 minutes flight time away. The AP was engaged and IMC prevailed.

Neither pilot remembered to cancel the FMS ‘HOLD’ mode “as they were engaged in some unnecessary conversation”. It was also noted that at this time, the Captain, an habitual smoker who had repeatedly failed to declare his habit on pilot medical self-declaration forms and repeatedly breached the company rule of no smoking in flight, had begun smoking another cigarette. The result of this oversight was that instead of continuing as cleared, when the aircraft reached GURAS, it turned left and began to enter the racetrack holding pattern. The Captain reacted by replacing ‘HOLD’ with ‘HDG’ and setting 027° to regain the required 022° track from the west aided by quite a strong westerly wind. The selection of HDG mode meant that pitch hold mode was also now active and the Captain responded by making pitch wheel inputs to initiate a descent at up to 1300 fpm.

Company stabilised approach procedures applicable to Kathmandu in Part ‘C’ of the OM were noted to require that full landing configuration with the landing checklist completed must be completed before the IAF (GURAS) whereas the Captain did not request initial flap 5 until 2 nm after this position and flap 15 until 4 nm DME after it. The landing checklist was similarly delayed and when ‘landing gear’ was called, the Captain responded with “gears down three greens” without checking to confirm. In fact it was not down and locked, a fact also “overlooked” by the First Officer. As the latter reported 10 miles final to APP and the flight was transferred to the TWR frequency, the CVR also recorded a continuous ‘landing gear unsafe’ tone on the area microphone channel which was being “constantly disregarded by both pilots”. Soon after this, the MDA for the approach was incorrectly set by the Captain as 4688 feet instead of the published figure of 4950 feet (equivalent to 629 feet above runway elevation). The Captain requested the landing checklist for a second time and the First Officer reminded him that it had been completed even though the landing gear unsafe tone was still sounding. The First Officer continued to prompt the Captain that they were descending at 500-600 feet above the procedure vertical profile.

The aircraft regained the VOR procedure final approach track (FAT) with just over 7 nm to go but this went undetected and the corrective left turn required - achievable by selecting LNAV or VOR mode - was not made. It was clear from the CVR that the Captain was having difficulty understanding what the First Officer was saying because of the high noise level on the flight deck created by the continuing landing gear status warning. The Captain was recorded asking for the landing checklist for a third time and again received the response that it was complete despite the continuing landing gear unsafe tone.

With the aircraft now in VMC, the MDA was reached with the descent rate still 1700 fpm and well to the right of the FAT as shown at annotated point 11 in the illustration below. Neither of the crew had the runway or even the “airport environment” in sight but no attempt was made to initiate a go around and the EGPWS Alerts ‘SINK RATE’ and ‘TOO LOW GEAR’ occurred (with no action taken by the Captain in response) as the TWR advised of a surface wind from 220° at 7 knots - a tailwind component of 6 knots - and cleared the flight to land. However, the alert appeared to result in the First Officer realising that the landing gear was not actually down and having sought permission from the Captain, she selected it down. The Captain then requested the landing checklist for a fourth time. The AP was disconnected as the aircraft passed east abeam the VOR which was located 0.7 nm prior to the 02 threshold. A further conversation between the pilots then “led to an ambiguous expectation of when they would acquire visual contact with the runway environment while being unaware that the aircraft had already flown past it” in a north easterly direction. The Captain appeared to continue assuming that the landing runway was still ahead of them even though it was now behind them to the south east and they were now 3-4 nm from the VOR.

TWR then called due to their concern at seeing the aircraft north east of the airport to remind them that they were supposed to be landing on runway 02 but appeared to be proceeding toward runway 20. The controller followed up by asking the crew what their intentions were and the Captain replied that they would be “landing on runway 02”. However, the aircraft continued to the north east until terrain ahead indicated that a right hand orbit was the only obvious way out. While struggling to find the runway, the flight continued on a north easterly track accompanied by “continuous EGPWS warnings with various flight parameters exceeded”. Sighting the rising terrain ahead, the Captain began a right hand orbit. During this manoeuvre, the aircraft descended to as low as 175 feet agl with bank angles of up to 35-40° leading to the activation of various EGPWS alerts and warnings.

The Investigation noted that although in VMC, neither pilot had yet seen the runway and were “desperate to find it” and still unaware of their position. The Investigation Commission “concluded that there had been a complete loss of situational awareness on the part of the flight crew at this stage”. The TWR controller called to confirm that the aircraft was still in VMC and that the crew still intended to position to land on runway 02 and, on receiving confirmation of both, cleared the flight to join right hand downwind for that runway. A caution that there was other traffic on short final for the same runway and ahead of them was given and acknowledged by the Captain.

However ATC then saw that the aircraft was tracking toward runway 20 instead of joining the right downwind for runway 02 as cleared and warned the crew not to proceed toward runway 20 because of the landing traffic and cleared them to perform “an orbit at their present position”. However, by this time, the aircraft had already flown north abeam the runway 20 threshold heading west and climbing. On reaching 6500 feet, the Captain then began to descend in a steeply banked right hand orbit northwest of the airport and was recorded “admitting to the First Officer that he had made a mistake as he was constantly talking to her”. The rate of descent exceeded 2000 fpm and the bank angle was as much as 45° right wing down which led to more EGPWS warnings. At 5,400 feet, the aircraft rolled out of the orbit onto a south easterly track still without having visually acquired the airport environment. Finally, with the other aircraft having now landed, and with no indication that either of the accident aircraft pilots had located the runway, the TWR controller, recognising the crew’s confusion over their position issued a landing clearance for either runway and assured them that the runway was clear. The Captain, who by now had completely taken over radio communications despite also hand flying the aircraft, replied that he would like to land on runway 20 but did not have it in sight. The CVR revealed that both pilots had made several statements which indicated that they completely lost any appreciation of their position relative to the runway.

The south easterly track was maintained through the extended runway 20 centreline and toward the area northwest of the runway 20 threshold and the TWR controller, unsure whether the crew had yet visually acquired the runway advised the aircraft’s position and suggested a turn to the right if it was not in sight. Whilst making this turn, the First Officer stated that she could see the runway at the 3 o’clock relative position when the aircraft was at about 1,200 feet aal and just under 2 nm from the 20 threshold. Despite the potential difficulty of manoeuvring directly to a landing from this position, the Captain attempted to do so, requesting that the heading bugs be set to 022 (instead of 202), calling for confirmation of landing clearance (received) and yet again calling for the landing checklist.

Those in the TWR then observed the aircraft still turning left from a westerly heading to align with the runway as it was about to reach the threshold. FDR data showed that it had crossed the threshold maintaining 150 KIAS at 450 feet agl and in a 40° banked turn with 35° to go until aligned with the runway. There was no call from the First Officer for a go around and the TWR controller, concerned that the aircraft turn was taking it west of the runway and close to buildings was alarmed by the situation and hurriedly sought to cancel the landing clearance previously given but instead transmitted "takeoff clearance cancelled". In the following 15-20 seconds, the aircraft flew over the area west of the runway as it turned left with continuous EGPWS ‘BANK ANGLE’ and ‘SINK RATE’ Alerts again sounding passing near the Tower and as low as 45 feet above the domestic passenger terminal before attempting to align with the runway for touchdown. Runway contact occurred 1700 metres along the 3050 metre-long runway with a bank angle of about 15° left wing down and on a heading of about 195°. The aircraft left the runway almost immediately and after breaking through the inner perimeter fence continued down a rough slope before coming to a stop about 440 metres from the first runway contact point. There was considerable impact damage and a major fire began almost immediately and engulfed much of the aircraft.

The Captain’s Performance

Recognising that the poor performance of the (senior) Captain was the main context for the accident, the Investigation documented various evidence that suggested that his mental health was such that he was unfit to be flying. Notwithstanding various findings, it was accepted that in the absence of any detected symptoms during any of the medical examinations which had followed his successful psychiatric re-evaluation in 2002, US Bangla had no general reason to be concerned about this issue medically. However, the extent to which he fully declared medically-relevant matters when completing medical self-disclosure forms was found to have varied which was considered to show that there was inconsistency between medical reality and medical disclosure.

It was also evident that he had been “talking almost non-stop” throughout the accident flight and had been worried and “emotionally stressed” about a particular interpersonal situation involving criticism of his competency by a colleague which had become widely known. On this latter subject, he could be heard telling the First Officer that he was so concerned by this situation that despite enjoying working for the airline and having no other job to go to, he planned to resign because of it. It was also noted from the CVR that he had at times been “irritable, tensed, moody, and aggressive” as an apparent consequence of this situation and it was considered that the stress of it may have induced the excessive and unnecessary conversation which had represented a significant distraction from focussing on the safe operation of the aircraft, in particular immediately prior to and during critical phases of flight.

The Probable Cause of the accident was determined as:

Disorientation and a complete loss of situational awareness on the part of the flight crew (after the intended) approach path was offset from the proper approach path leading to manoeuvres in a very dangerous and unsafe attitude to align with the (opposite direction of the) runway. The landing was completed in sheer desperation after sighting the runway at very close proximity and very low altitude (and with) no attempt made to carry out a go around when a go around seemed possible until the last instant before touchdown on the runway.

A total of 20 Contributory Factors were also identified:

1. The inappropriate timing of the (dispatcher’s) operational pre-flight briefing for the accident flight which was given in early morning when the flight departure time was around noon and there were four short domestic flights scheduled first.
2. The Captain, who was the PF, seemed to be under stress due to the behaviour of a particular female colleague in the company (not present on the flight) and lack of sleep the preceding night.
3. A very steep authority gradient between the two pilots.
4. The flight crew not having practiced a visual approach for runway 20 in the simulator.
5. A poor level of CRM between the two pilots.
6. The failure to arm the VOR so that the autopilot would intercept the desired radial (the aircraft never established on the procedure radial, rather it passed through it from left to right because HDG Mode remained selected).
7. The failure to adhere to standard operating procedure including the failure to perform a proper briefing.
8. The fact that the unsafe gear warning horn was not noticed by the crew until approaching the MDA of the initially attempted VOR approach procedure.
9. The Captain did not promptly respond to EGPWS Warnings with corrective action.
10. The failure to carry out a standard missed approach procedure from the initial approach to runway 02 despite the runway not being in sight at MDA.
11. The failure to meet the criteria for stabilised approach.
12. The Captain’s increased workload when he was manually flying the aircraft whilst also communicating with ATC.
13. A loss of situational awareness due to mis-alignment with the runway during initial approach and subsequently not being able to sight the runway.
14. The high bank angle, rapid rate of descent, excessive threshold speed and inadequate rudder input contributed to a hard contact of the right main landing gear with the runway.
15. The failure to monitor the speed, altitude and the radial during the initial approach attempt.
16. A lack of assertiveness on the part of the Air Traffic controller when monitoring the flight path of the aircraft and not then issuing a clear instruction to carry out a standard missed approach procedure.
17. A lack of clear understanding and acknowledgment on the part of both ATC and the flight crew in respect of each other's communication regarding the landing runway.
18. A failure on the part of the ATC to alert the crew to their actual position.
19. Although the First Officer was operating to Kathmandu, a Category ‘C’ airport, for the first time, no safety pilot, which could have been a great help in the situation, was provided.
20. A lack of simulator training for the Captain dedicated to the visual approach for runway 20 at Kathmandu.

A total of 15 Safety Recommendations were made by the Investigation Commission as follows:

• that the Bangladesh CAA should, before renewing the licence of any pilot who has previously been permanently grounded for medical reasons, require a thorough assessment of their physical and psychological status. A system which will closely monitor their medical condition in all subsequent medical examinations should be adopted as well.
• that the Bangladesh CAA should require all airline pilots to undergo a psychological evaluation as part of their training or before entering into the service and airlines shall verify that the evaluation has been carried out. The psychological part of the initial and recurrent aeromedical assessment and the related training for aeromedical examiners should be strengthened.
• that US Bangla Airlines should give emphasis to the proper and effective implementation of CRM in the company.
• that US Bangla Airlines should establish a system to ensure the proper implementation of SOPs in all phases of flight.
• that US Bangla Airlines should establish an effective mechanism to monitor and assess the mental health status of pilots in respect of professional development and financial issues as well as personal and psychological issues.
• that US Bangla Airlines should establish and implement a policy to de-roster any crew member found to be stressed, fatigued or emotionally disturbed.
• that US Bangla Airlines should re-examine its system to ensure that all relevant documents are subject to timely review and updating.
• that US Bangla Airlines should revise their pilot training process to include simulator training for the circling approach to runway 20 at Kathmandu.
• that US Bangla Airlines should re-assess its pre-flight briefing regime to ensure that a proper pre-flight briefing by the dispatcher to the crew has been given at the appropriate time.
• that US Bangla Airlines should revise their training programme to include the provision of a safety pilot during Kathmandu route clearance training for less experienced pilots.
• that US Bangla Airlines should ensure that Line Oriented Safety Audits (LOSA) are carried out periodically.
• that US Bangla Airlines should encourage crew members to be specific regarding the reporting of their medical issues and habits on the medical self-declaration form.
• that US Bangla Airlines should reinforce a firm policy regarding No Smoking during the flight and have a system in place to monitor compliance proactively and take any necessary action accordingly.
• that the CAA Nepal should strengthen the capacity of the air traffic controllers by developing an appropriate training programme to enable them to become more assertive when handling traffic and issuing clearances to such traffic especially in the event of abnormal or emergency situations.
• that the CAA Nepal shall require air traffic controllers to be more vigilant and visually look out for an aircraft after its landing clearance has been issued in VMC.

The Final Report of the Investigation was published on 27 January 2019.

Related Articles

• Pilot Mental Health
• Situational Awareness
• Crew Resource Management (CRM)
• Line Operations Safety Audit (LOSA)
• Authority Gradients
• Interruption or Distraction
• Stress
• Runway Excursion
• Circling Approach
• Non-Precision Approach
• Pilot Workload
• VFR Loss of Positional Orientation: Guidance for Controllers
• Guidelines for Dealing with Unusual/Emergency Situations in ATC
• Vigilance in ATM