ASN Wikibase Occurrence # 150750
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| Date: | Monday 25 April 2011 |
| Time: | 07:50 |
| Type: |  Boeing 737-8AS (WL) |
| Owner/operator: | Ryanair |
| Registration: | EI-DAD |
| MSN: | 33544/1249 |
| Year of manufacture: | 2002 |
| Fatalities: | Fatalities: 0 / Occupants: 179 |
| Aircraft damage: | None |
| Category: | Serious incident |
| Location: | near Skavsta airport -
 Sweden
|
| Phase: | Initial climb |
| Nature: | Passenger - Scheduled |
| Departure airport: | NYO - ESKN |
| BVA - LFOB | |
| Investigating agency: | SHK |
| Confidence Rating: |  Accident investigation report completed and information captured |
Summary
On 25 April 2011, shortly after take-off, a Ryanair Boeing 737-800 received an indication
that one of the aircraft's two electrical systems had lost electrical power. This
had been preceded by one of the two generators that supply electrical power to the
aircraft being disconnected, upon which redistribution took place so that the other
generator supplied power to both electrical systems. An electronic monitoring and
control unit automatically ensured that this took place.
The pilots followed the checklist and attempted to reconnect the generator. They also
attempted to connect the generator from the Auxiliary Power Unit (APU). Either during
the attempt to reconnect the disconnected generator or the connection of the auxiliary
power unit's generator, the connection between the two systems was broken, with
the consequence that one of the systems
lost electrical power.
The pilots made a further attempt to reconnect a power source but were unsuccessful.
The decision was therefore made to return and land at Skavsta Airport. Flying with
one of the electrical systems not having power meant among other things losing the
display of flight instruments on the affected side. Flap indication and pitot heating
were among the systems which lost their power supply and stopped working during
the incident.
The electronic monitoring and control units are intended to ensure that both electrical
systems are always supplied with power as long as there is at least one power source
available. They are also intended to prevent electrical interconnection of the electrical
systems when each subsystem is supplied by its own power source. The control units'
commands are based on status signals from relays, among other things.
The incident was caused by the system logic for the Generator Control Unit (GCU)
and the Bus Power Control Unit (BPCU) enabling erroneous status signals from the
breaker (Generator Control Breaker, GCB) to lead to a transfer bus losing power.
Accident investigation:
 |
|
Sources:
http://www.havkom.se/virtupload/reports/RL2012_20e.pdf SHK investigation report
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 18-Nov-2012 12:24 | Masen63 | Added |
Corrections or additions? ... Edit this accident description
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