Lauda Europe A320 at London on May 28th 2021, abnormal engine behaviour
Last Update: June 9, 2022 / 09:20:56 GMT/Zulu time
On Oct 21st 2021 the British AAIB reported the aircraft experienced "abnormal behaviour of the No.2 engine and associated cockpit indications during approach.", rated the occurrence a serious incident and opened an investigation.
The aircraft had last flown a traffic circuit around Stansted on Feb 28th 2021 and had done its last revenue flight on Nov 29th 2020 from Vienna (Austria) to London Stansted. Following the occurrence the aircraft returned to service on Jun 5th 2021 and has been flying ever since.
On Jun 9th 2022 the AAIB released their final bulletin with no conclusion to the actual cause of the occurrence rated a serious incident.
The AAIB analysed:
The manufacturer’s assessment of the failure messages seen on the post-flight report and the ECAM warning was that they were consistent with the reduction in EPR caused by an uncommanded activation of the overspeed protection valve in the FMU. This reduced the fuel flow to the engine to a fixed level which was just below flight idle. The flight data values recorded for N1 and N2 immediately prior to this were normal and confirmed that no actual overspeed had occurred, which would have resulted in the valve correctly operating.
Once activated, the fixed flow rate through the overspeed protection valve cannot be varied by any input from the throttle or the FMGC. As such, the apparently frozen parameters reported by the flight crew were an accurate indication of the engine status.
The other ancillary engine indications and associated systems’ operating parameters recorded by the DFDR were all consistent with this. The valve remained hydraulically latched while the engine was operating but would have reset after the engine was shut down. The final overspeed protection fault warning seen on the post-flight report is intentionally inhibited by the system until after touchdown and the aircraft airspeed has reduced below 80 kt, which is why it appeared to occur after the engine had been shut down. The previous in-service events where the overspeed protection valve had operated without being commanded by the EEC, were very similar to this incident involving 9H-LOZ.
It was not possible to confirm a definitive root cause for the activation of the overspeed protection valve from the evidence recovered by the investigation. However, these events are all the subject of ongoing continued airworthiness activities by the engine and aircraft manufacturers.
The AAIB described the sequence of events:
The aircraft was scheduled to conduct a preservation flight1
on 28 May 2021, departing from and returning to Stansted Airport and lasting approximately 45 minutes. The operating crew positioned from Vienna to Stansted as passengers on a commercial flight, arriving in the crew room at Stansted at 0630 hrs. They waited for the morning engineering shift to come on duty at 0700 hrs and the aircraft was handed over to them shortly afterwards. The crew conducted the standard walkaround and pre-departure checks with no abnormal findings. The aircraft departed from Stand 33L at 0803 hrs after a normal engine start and pushback and taxied to line up and hold on Runway 22.
Whilst holding on the runway, the crew were requested by Air Traffic Control (ATC) to consider a new Standard Instrument Departure (SID) route, but they declined this request to avoid the need to re-brief the departure whilst positioned on an active runway. They were given clearance to take off and climb to FL080 following the CLN1E SID, which they completed without issue. They were subsequently given radar vectors to line up for an ILS approach to land back on Runway 22.
During the final approach, at 950 ft radio altitude and with autothrust engaged, an ‘eng 2 fadec fault’ appeared on the Electronic Centralised Aircraft Monitor (ECAM). The crew elected to go around and manually flew the standard missed approach profile, before entering a hold to perform troubleshooting of the fault. During this period the No 2 engine remained at idle despite manual throttle increases and the reselection of autothrust. The crew also reported seeing apparently erroneous engine parameter readings relative to the selected throttle position. After entering the hold, the immediate ECAM checklist actions were performed. The crew reported that the engine indications were not showing amber XX, but appeared to be frozen and were still not responding to any throttle inputs. The ECAM checklist directed that in the case of abnormal engine parameters the engine should be shut down. The crew consulted the Flight Crew Operating Manual (FCOM) for further guidance, before starting the Auxiliary Power Unit (APU) and shutting down the No 2 engine.
The crew declared a MAYDAY and selected squawk 7700. They then briefed for a return to Runway 22 at Stansted. After completing all the necessary single-engine operation checklists and landing performance calculations, they requested radar vectors for a normal ILS approach to Runway 22. Following an uneventful approach and landing, the aircraft vacated the runway and the crew confirmed with the Airport Fire and Rescue Service Commander that the failed engine appeared normal. During the landing rollout as the aircraft airspeed dropped below 70 kts an ‘eng 2 ovspd prot fault’ warning was triggered but this was not displayed on the ECAM. The aircraft was then taxied to Maintenance Hangar 10 at Stansted and shut down in accordance with the relevant checklists.
This article is published under license from Avherald.com. © of text by Avherald.com.
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