ASN Wikibase Occurrence # 216394
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| Date: | Thursday 3 May 2018 |
| Time: | 22:10 UTC |
| Type: |  British Aerospace ATP |
| Owner/operator: | West Air Sweden |
| Registration: | SE-MHF |
| MSN: | 2013 |
| Year of manufacture: | 1989 |
| Engine model: | Pratt & Whitney Canada PW126 |
| Fatalities: | Fatalities: 0 / Occupants: 2 |
| Aircraft damage: | None |
| Location: | 8 nm west of Milton Keynes, Buckinghamshire -
 United Kingdom
|
| Phase: | En route |
| Nature: | Cargo |
| Departure airport: | London-Stansted Airport (STN/EGSS) |
| East Midlands Airport (EMA/EGNX) | |
| Investigating agency: | AAIB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The aircraft was operating a cargo flight from East Midlands Airport to Stansted Airport and was established in the cruise at FL110 with the No 2 autopilot engaged. The co-pilot was the pilot flying and the commander was the pilot monitoring. As the aircraft was approximately 8 nm west of Milton Keynes and, shortly before commencing the descent towards Stansted Airport, the master caution aural alert sounded and the TRU 1 and dc lo volts central warning panel (CWP) lights illuminated. This indicated that the No 1 TRU was no longer supplying 28 VDC voltage to the No 1 essential DC busbar.
The crew carried out Emergency and Abnormal Checklist (EAC) Card 49 ‘TRU failure or single DC busbar low voltage’. The commander initially attempted to reset TRU 1, but this was not successful. He then switched the No 1 non-essential DC busbar off and selected the DC essential busbar couple to connect the No 1 and No 2 essential DC busbars together. Following these selections, the dc lo volts warning message extinguished, and the crew observed that the No 1 battery voltage indicator was in the green arc, indicating that the battery voltage was between 23 and 29 V. During this period, the commander was recorded on the CVR stating that he considered it was a busbar relay fault, rather than a TRU fault.
The crew decided to return to East Midlands Airport. Shortly after, the commander tried to reset the TRU 1 again but this was unsuccessful. En-route the crew confirmed that the load on the No 2 TRU was below 180 amperes (A) and that no circuit breakers in the cockpit had tripped.
Approximately 15 minutes after the initial loss of electrical power, the commander noticed that his flight director had failed. The crew confirmed that the DC essential busbars were coupled and the dc lo volts CWP caption had re-illuminated. The commander subsequently recalled that the No 1 inverter had failed and the No 1 battery voltage had reduced to 12V.
Seven minutes later, a master caution alert sounded and the gpws CWP caption illuminated. This was shortly followed by the commander’s electronic flight instrumentation system (EFIS) primary flight display (PFD) and navigation display screens becoming corrupted and unreadable and the autopilot disconnecting; the quick access recorder (QAR) recording also stopped. The commander then declared a PAN.
A few minutes later, as the aircraft was descending to 5,000 ft amsl, the No 1 engine control frozen indication and standby controls fail CWP caption illuminated, the flight deck lights flickered and a pulsing was heard on the radio by both crew. As a precaution, the crew advised ATC that the radios might stop operating. The FDR stopped recording a few seconds later. The commander selected the emergency busbar for his radio (the co-pilot’s was also supplied by the emergency busbar) but the pulsing sound continued.
The aircraft was on base leg for runway 27 at East Midlands Airport when the flight management system (FMS) failed, along with the No 1 DME and the autopilot flight mode annunciator panel. When the aircraft was about 7 nm from the runway, the pulsing sound on the radios stopped. The aircraft was vectored to a visual approach to runway 27, which was followed by an uneventful landing, flown by the co-pilot whose EFIS screens were operating normally. As the aircraft touched down, the pulsing sound on the radios briefly returned before stopping again.
As the aircraft vacated the runway, the dc lo volts and tru 1 CWP warning messages extinguished and power was restored to the flight deck lights, the commander’s EFIS screens and flight director. The crew checked the electrical load on TRU 2 and noted that it was more than 180 A, so they followed QRH Card 49 again. The crew selected the inverter transfer on and selected inverter No 2 and both non-essential DC busbars off, to reduce the electrical load, and the DC essential busbars were confirmed as being coupled.
After the aircraft was parked, the crew and two engineers from the operator’s maintenance organisation discussed the event and began fault-finding. As the No 1 battery busbar was connected to DC power, the No 1 battery overheat CWP caption briefly illuminated and one engineer noted that the No 1 battery was drawing over 300 A. Both batteries were switched off prior to further functional testing of the electrical power system.
AAIB Conclusion:
The aircraft experienced two separate, independent failures within the DC electrical power system during a cargo flight from East Midlands Airport to Stansted Airport, resulting in the loss of multiple flight deck instruments, lighting, left engine control and standby flying controls. The crew were able to return to East Midlands Airport where a normal landing was made, following which the DC electrical power was restored. The loss of electrical power experienced during the flight was consistent with a failure of the No 1 TRU or its contactor, followed by a subsequent failure of the DC essential busbar couple function.
The cause of both failures, which could not be repeated during subsequent testing, was probably intermittent and transitory so could not determined.
Accident investigation:
 |
|
Sources:
1. AAIB Final Report: https://assets.publishing.service.gov.uk/media/5cb70035ed915d06935f9490/British_Aerospace__BAe__ATP_SE-MHF_05-19.pdf
2. https://www.havkom.se/en/investigations/civil-luftfart/tillbud-med-ett-flygplan-av-typen-british-aerospace-bae-atp-i-samband-med-landning-pa-east-midlands-airport-i-storbritannien
3. https://www.planelogger.com/Aircraft/Registration/SE-MHF/679368
4. https://www.planespotters.net/airframe/British-Aerospace/BAe-ATP/SE-MHF-West-Air-Sweden/ANl6Hxxl
5. http://forum.flyghistoria.org/viewtopic.php?f=16&t=15630
History of this aircraft
Other occurrences involving this aircraft
| 7 October 2014 | G-BTPF | Atlantic Airlines | 0 | near Bournemouth Airport, Parley Lane, Christchurch, Dorset | |
non |
| 14 December 2017 | SE-MHF | West Air Sweden | 0 | East Midlands Airport (EMA/EGNX) | |
non |
Media:
_(17037583420).jpg)
British Aerospace ATP, loss of electrical power and moisture in flight data recorder, 3 May 18https://t.co/ftLT61Huv5 pic.twitter.com/KES0tjfz8j
— AAIB (@aaibgovuk) 25 April 2019
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 18-Oct-2018 22:55 | Dr.John Smith | Added |
| 18-Mar-2019 14:01 | Aerossurance | Updated [Location, Departure airport, Narrative] |
| 28-Apr-2019 07:24 | harro | Updated [Time, Operator, Total occupants, Location, Phase, Damage, Narrative, Accident report, ] |
| 28-Apr-2019 07:25 | harro | Updated [Embed code] |
| 09-May-2019 18:26 | Dr. John Smith | Updated [Location, Source, Narrative] |
| 10-May-2019 01:02 | Dr. John Smith | Updated [Embed code, Narrative] |
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