On 21 June 2017, the number 2 CFM56-5B engine of an Airbus A320 (VT-GOS) being operated by GoAir on a scheduled domestic passenger flight from Delhi to Mumbai as G8-338 began to malfunction during the takeoff roll. The takeoff was continued but once airborne in day VMC, the serviceable number 1 engine was shut down and TO/GA thrust set on the malfunctioning number 2 engine. An emergency was declared and an immediate return requested and approved. Whilst the critical error was being identified and addressed, the airspeed dropped sufficiently for ALPHA floor protection against excessive angle of attack to be activated. A recovery to controlled flight with the malfunctioning number 2 engine set to idle was eventually achieved and on the second attempt a visual approach and landing back at Delhi was accomplished. Once parked, fan blade damage to the right engine which was subsequently attributed to a bird strike could be seen.
An Investigation was carried out by the Indian DGCA in accordance with the Aircraft Accident Investigation of Accidents and Incidents Rules 2012. Data from the CVR and FDR were successfully downloaded and together enabled a detailed reconstruction of the sequence of events.
It was noted that the 64 year-old Captain, who had been PF for the flight, had a total of 23,507 hours flying experience which included 13,187 hours on type. He had only returned to flying in command 5 days prior to the investigated event after being declared “temporarily medically unfit for flying” on a number of occasions between February 2014 and March 2017. Prior to this he had been authorised as a Check Pilot on type. His initial return to line flying had been a 20 day period as a First Officer after which flying in command had been conditional on being paired with a “qualified experienced pilot”. The 30 year-old First Officer had 936 hours total flying experience which included 730 hours on type. It was observed that “as per records available”, the First Officer met the (unstated) requirements for a “qualified experienced pilot”. It was noted that the same crew had earlier operated uneventful sectors from Bangalore to Mumbai and from Mumbai to Delhi in the same aircraft.
Using the recorded data available, it was established that with the applicable V1/Vr/V2 calculated respectively as 146/146/147 KIAS, the takeoff roll had proceeded normally until approximately 115 KIAS at which point a bird was, unknown to the crew, ingested into the right engine as a result of which the vibration level for that engine immediately rose to 5.2 and engine-source vibration became obvious to both pilots. Passing 129 KCAS, the vibration level had reached 9.9 and an ECAM Advisory Message for high N1 vibration on the right engine was annunciated. Although this was not called by the First Officer, he immediately asked the Captain if he wanted to reject the takeoff to which the Captain responded “no”. Lift off subsequently occurred at 155KCAS and the aircraft was “fully airborne” at 163 KCAS.
Once safely climbing, the First Officer called “engine vibration no 1 out of limits”, having mixed engine no 1 with N1 on the lower ECAM display (see the illustration below). The Captain did not confirm this by inspection and as the aircraft approached 2200 feet QNH (the Delhi ARP elevation in 777 feet) he almost immediately selected the thrust on serviceable engine number 1 to Idle and increased the thrust on unserviceable engine 2 to CLIMB and then to TO/GA. At 2700 feet QNH, engine 1 was shutdown and the crew declared an emergency to ATC requesting an immediate return. Airspeed at this point was recorded as 152 KCAS and the previously engaged AP disconnected due to turbulent conditions. ATC responded accepting the request and telling the crew to stop climb at 3000 feet - the aircraft was levelled at 3300 feet.
The lower ECAM display with vibration levels below engine oil pressure and temperature. [Reproduced from the Official Report]
Even after the Captain had shut down the wrong engine, the First Officer’s confusion continued and it was two minutes before the Captain, concerned that the vibration had not reduced after engine 1 had been shut down, checked the ECAM display himself and realised the error. The crew set about restarting the number 1 engine without using the checklist and failed to open the cross bleed valve so that the attempt failed. With the number 2 engine now set to idle and with the AP now re-engaged, the attempt to maintain 3,300 feet with no engine thrust resulted in an un-noticed progressive reduction in airspeed. A second restart attempt with the cross bleed valve in the correct open position and the malfunctioning number 2 engine returned to ‘CLIMB’ was successful and four minutes after the number 1 engine had been shut down, it was producing useful thrust again.
During the restart process, the AP again disengaged in turbulence with the airspeed now 127 KCAS and by the time the number 2 engine had been returned to Idle and the number 1 engine had been set to ‘CLIMB’, 300 feet of height had been lost and the aircraft was now 1,986 feet agl. The angle of attack reached the threshold for the A/T to apply ALPHA FLOOR protection and TO/GA thrust was set (on both engines) automatically. The ‘TO/GA Lock’ annunciation which indicated an exit from ALPHA FLOOR conditions appeared after 24 seconds and by the time this mode had been cancelled by disconnecting the AP and A/T, the airspeed was 223 KCAS but aircraft altitude was down to 2,600 feet (1,563 feet agl). After a total of six minutes with the number 2 engine vibration above the ECAM Advisory trigger of 6 and having reached a maximum value of 9.9, this indication reduced to 5.3 and eventually, with the engine set to idle, to 1.2 and remained low for the remainder of the flight.
During the next four minutes, the aircraft was vectored onto the ILS LLZ for runway 10 but soon after landing clearance had been given, the crew initiated a go around because they were too high. This was conducted with the number 1 engine set to FLX/MCT and the number 2 engine remaining at Idle. The second approach led to an uneventful landing. However, whilst taxiing in to its allocated stand, the aircraft took a wrong turn and had to be towed there with its engines both shut down. Once on stand, it was visually apparent that the number 2 engine had sustained fan blade damage due to a combination of bird ingestion and continued operation at high vibration levels. The two affected blades were replaced and after no other damage was found, the engine was returned to service subject to a precautionary borescope inspection after the first of 10 flights or 25 hours.
Number 2 engine fan blade damage (left) and bird blood stains (right). [Reproduced from the Official Report]
Although the Captain made a contrary entry in the Aircraft Technical Log after completion of the flight, the landing was marginally overweight at 64,770kg against an MLW of 64,500kg. His complete post flight Technical Log entry was noted to have been “Return Back due to High Vibration Engine Number 2. Overweight LDG not applicable. ENG parameter normal”. The absence of any reference to continued operation of the number 2 engine at excessive vibration levels and to any birdstrike was noted - although it was recognised that the crew had no awareness of the bird strike whilst in flight. It was not possible to identify the bird species ingested on the basis of only its blood and the engine damage caused.
It was noted that despite having just been involved in what was self-evidently a Serious Incident, the flight crew were then allocated another aircraft VT-WAF and operated the same flight, G8-338 to Mumbai.
The Investigation catalogued a series of crew actions/inactions over the course of the flight which had not been in accordance with SOPs. These included:
- Neither the Takeoff nor After Takeoff Checks were completed.
- The QRH procedure for high engine vibrations was not followed - the Captain shutdown the number 1 engine without reference to the QRH.
- The engine in flight re-light procedure was not followed.
- The Captain’s post-flight Technical entry was both incomplete and in part incorrect.
More generally, it was concluded that:
- Both pilots lacked adequate situational awareness and had demonstrated poor Cockpit Resource Management while handling the emergency.
- While re-starting number 1 engine, neither pilot noticed the decreasing speed of the aircraft.
- Aircraft handling during the emergency was neither effective nor appropriate.
Bird Hazard Management
Whilst no specific problems were identified with the effectiveness of Wildlife Hazard Management arrangements at the airport, it was noted that the number of recorded bird strikes had increased substantially between April 2017 and August 2017. It was also noted that the Airfield Environment Management Committee, which was responsible for “unresolved bird hazard/environmental problems” had not been meeting at the intervals prescribed by the “Aerodrome Administration and Safety Management System”.
The Probable Cause of the event was determined as “incorrect identification of the engine affected by high vibration followed by non-adherence to recommended procedures, lack of situational awareness, poor Cockpit Resource Management and poor handling of aircraft during an emergency subsequent to a bird strike”.
Three Safety Recommendations were made as follows:
- that DGCA Headquarters should determine suitable corrective action for both crew members in view of the findings of the Investigation.
- that Delhi International Airport should be advised to adhere to the programmes & procedures outlined in their Aerodrome Manual considering the above findings.
- that Delhi International Airport should ascertain the effectiveness of their existing Wildlife Hazard Management Plan and review its content if deemed necessary.
The Final Report was completed on 5 November 2018.