"Fulle av feil" er å ta hardt i, men jeg er alvorlig lei av at sertifiserende myndigheter sertifiserer fly med feil. Det gjelder både Airbus og Boeing produkter. Det skal for søren ikke være slik. (Red.)
Airbus A350 software forces airlines to turn planes off and on every
149 hours
Patch your darn metal bird, sighs EU aviation
agency
Airbus A350-1000
An Airbus promotional
picture of an A350-1000. Its sister type, the A350-941, is the affected model of
airliner
Some models of Airbus A350 airliners still need to be hard
rebooted after exactly 149 hours, despite warnings from the EU Aviation Safety
Agency (EASA) first issued two years ago.
In a mandatory airworthiness
directive (AD) reissued earlier this week, EASA urged operators to turn their
A350s off and on again to prevent "partial or total loss of some avionics
systems or functions".
The revised AD, effective from tomorrow (26 July),
exempts only those new A350-941s which have had modified software pre-loaded on
the production line. For all other A350-941s, operators need to completely power
the airliner down before it reaches 149 hours of continuous power-on
time.
Concerningly, the original 2017 AD was brought about by "in-service
events where a loss of communication occurred between some avionics systems and
avionics network" (sic). The impact of the failures ranged from "redundancy
loss" to "complete loss on a specific function hosted on common remote data
concentrator and core processing input/output modules".
In layman's
English, this means that prior to 2017, at least some A350s flying passengers
were suffering unexplained failures of potentially flight-critical digital
systems.
Airbus' rival Boeing very publicly suffered from a similar
time-related problem with its 787 Dreamliner: back in 2015 a memory overflow bug
was discovered that caused the 787's generators to shut themselves down after
248 days of continual power-on operation. A software counter in the generators'
firmware, it was found, would overflow after that precise length of time. The
Register is aware that this is not the only software-related problem to have
plagued the 787 during its earlier years.
It is common for airliners to
be left powered on while parked at airport gates so maintainers can carry out
routine systems checks between flights, especially if the aircraft is plugged
into ground power.
The remedy for the A350-941 problem is straightforward
according to the AD: install Airbus software updates for a permanent cure, or
switch the aeroplane off and on again.
Flying down the rabbit hole
An
Airbus marketing publication (PDF) from 2013 explains that the A350's Common
Remote Data Concentrator (CRDC) units were designed to "allow significant wiring
simplification", with an aerospace trade mag going into greater depth to explain
that Airbus' newest airliner design features 29 CRDCs "spread around the
aircraft" and working in concert with 21 Core Processing Input Output Module
(CPIOM) modules, interfacing with various systems and sensors.
CRDCs take
input data (say, the exact position of a flight control surface) and turn that
into an ARINC 429-compatible digital signal for transmission over the A350's
internal network to a CPIOM. That network runs over a protocol developed by
Airbus called ADFX, or Avionics Full-Duplex Switched Ethernet. The CPIOM is
effectively a mini computer; in the A350 CPIOMs run discrete avionics
"applications", in the sense of apps. CRDCs themselves do not host or run
applications, suggesting that the failure condition detailed in the EASA AD may
mean loss of a particular app on a CPIOM after a buffer overflow.
A Delta
Airlines training manual on Scribd, of all places, explains what the A350's
CPIOM apps are. They include: the fuel quantity and management system, which
tells pilots how much juice their bird has drunk; the cabin pressure control
system; wing ice protection systems; the engine bleed air system, which among
other things supplies oxygen to the passenger cabin for you to breathe; and the
landing gear extension and retraction system.
Excerpt from A350 avionics training
manual
Airlines acquiring the A350-941 model subject to the EASA AD
include Air France, American Airlines, Delta Air Lines and Lufthansa, as well as
Air China and Taiwan's China Airlines. Both British Airways and Virgin Atlantic
are buying A350-1041s, which are a different model from the affected
A350-941s.
There are no A350s (ICAO codes A359 and A35K) currently on the
UK register, though registrations have been reserved for those being acquired by
British airlines.
Airbus PR reps failed to respond to multiple requests
for comment.
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