Hope Keiron and the folks at ATI don't mind but they have put something together that does clear up some queries. Obviously we all await the eventual official reports but this is the best precis I've seen of what is known publicly at the moment.
Flameout stopped A330's FDR & CVR for last 20min of flight
Chris Kjelgaard, Washington DC (04Sep01, 22:44 GMT, 633 words)
Portuguese and Canadian safety officials investigating why an Air Transat
Airbus A330-200 had to make an unpowered landing in the Azores on 24 August
will be unable to derive any information from the aircraft's flight
recorders for the last 20min of the flight.
The Transportation Safety Board (TSB) of Canada confirms the flameout of
both of the A330's engines stopped the supply of electrical power to its
alternating current (AC) power buses. As in many other commercial aircraft
types, the AC buses in the A330-200 provide the electricity supply to power
both the digital flight data recorder (DFDR) and the cockpit voice recorder
(CVR).
The A330's AC power buses are supplied with electrical current by the
generators attached to each engine and by the aircraft's auxiliary power
unit (APU). In the Air Transat incident, however, the engines flamed out
because of fuel starvation following a serious fuel leak and the draining of
all fuel also meant the pilots of the aircraft were unable to use the APU to
provide electrical power.
The initial findings of the investigation, led by the Portuguese civil
aviation agency INAC, show the A330's right engine - the engine in whose
fuel supply the leak occurred - flamed out at 06:13 GMT on 24 August, but
that the left engine of the aircraft remained lit for another 13min, until
06:26 GMT.
At this point the A330 was still at an altitude of 34,000ft and was 85nm
distant from Lajes airport on the island of Terceira, at which it landed at
06:46 GMT after gliding without engine power or main electrical power for 20
min. At 06:39 GMT, 7min before landing, the aircraft was still at an
altitude of 13,000ft and was 8nm from the threshold of Lajes airport's
runway 33.
Neither the DFDF nor the CVR was operational during the last 20min of the
flight as a result of the loss of electrical power. This is not preventing
the officials investigating the incident from using the readouts from the
recorders in trying to piece together why both engines flamed out, as the
data from the period before the fuel ran out is likely to be of more
immediate importance in finding out what went wrong than what happened
afterwards.
Nevertheless, one official says that as well as understanding the Air
Transat crew's actions during the last 20min of the flight, the
post-flameout data could have been of considerable use to the investigating
agencies in modeling the flight characteristics and systems behavior of the A330 for future simulations of the aircraft in conditions of unpowered
flight.
The TSB has been concerned about interruptions in power supply to flight
data recorders of commercial aircraft ever since it began its investigation
into the crash of a Swissair MD-11 off the coast of Newfoundland in
September 1998.
In its first safety action arising from the Swissair Flight 111
investigation, the TSB recommended on 9 March 1999 that from 1 January 2005
every aircraft with a CVR offering a recording capacity of at least 2h
should have an independent power supply to power the CVR and the cockpit
area microphone for a period of 10min.
This power supply would allow the microphone and CVR to keep working
whenever the normal power source to each was interrupted.
§
The TSB also recommended that in aircraft required to have two flight
recorders, each recorder should be powered by a separate generator bus, to
minimize the possibility of an interruption in the power supply from one bus
affecting the recording capabilities of both the recorders.
In its Swissair 111 recommendations the TSB did not specifically address the
need for the DFDR in each aircraft to be linked to an independent power
supply, but the agency might review its position as a result of the findings
of the Air Transat incident.
Source: Air Transport Intelligence news
[ 05 September 2001: Message edited by: PPRuNe Towers ]