Shortly after commencing descent from flight level (FL)310, the
pilot of the Cessna Conquest noticed that the cabin altitude
indication was rising. When passing through FL270, the cabin rate
of climb rose to 3,000 ft/min with an accompanying decrease in
cabin differential pressure and both master warning and "ALT"
annunciators illuminating. When the annunciator lights illuminated,
the pilot observed that the cabin oxygen masks failed to
auto-deploy at this time as required. As the patients were already
on oxygen and the flight nurse had donned a spare mask, he did not
deploy the cabin masks manually. The pilot donned his own oxygen
mask and commenced a rapid descent to 10,000 ft.
The pilot reported that the cabin altitude indication increased to
a peak of 17,000 ft before decreasing during the descent. A
subsequent maintenance inspection found water contamination present
in the cabin door seal pressurisation solenoid valve and it was
suspected that this water froze, preventing the correct operation
of the valve.
The failure of the oxygen mask auto-deployment system was also
investigated and the wiring to the barometric activation switch was
found to have a high resistance. This wiring was replaced. As a
precaution, the wiring to the barometric switch that activated the
cabin altitude annunciator warning light was also replaced. During
these rectifications, the maintenance personnel discovered that
there was no procedure published by the manufacturer to correctly
adjust and test either barometric switch set point after
maintenance.
A sampling of maintenance manual procedures for aircraft types
manufactured in countries such as the United States, United Kingdom
and Switzerland was carried out. This sampling concluded that the
maintenance deficiency for test and return to service of the oxygen
deployment and cabin altitude alert barometric switches, found in
the occurrence aircraft maintenance procedures, was also apparent
in all but one of the other aircraft type manufacturer's
maintenance procedures.
Safety Recommendation
The Australian Transport Safety Bureau
recommends that the Australian Civil Aviation Safety Authority
liaise with the United States Federal Aviation Administration, the
United Kingdom Civil Aviation Authority and the European JAA on
implementation strategies to address these safety deficiencies.
The Civil Aviation safety Authority (CASA) wrote to the United
States FAA, the European JAA, UK CAA and NZ CAA on 31 July 2002
inviting liaison on the safety deficiencies identified in
Occurrence Brief 200200095. Questions were also asked about these
authorities' views and intentions regarding periodic maintenance of
barometric switches in pressurised aircraft.
The following response dated 29 November 2002 was received from
CASA on 03 December 2002:
Thank you for providing a copy of aviation Occurrence Brief
200200095 on the incident involving Cessna 441 Conquest VH-NFD
which occurred 22km north west of Perth VOR, Western Australia on
31 January 2002.
In its response to the draft Brief, the Authority, in respect of
Recommendations R20020101 and R20020102, stated that:
CASA intends raising an Airworthiness Bulletin (AWB) to provide
advice on how this feature may be incorporated into maintenance
documentation covering periodic maintenance of barometric pressure
switches in Australian registered pressurised aircraft. CASA's
long-term approach will be influenced by the response of other
aviation authorities to the liaison initiated by CASA as the result
of Recommendation 20020109.
The AWBs have been published as AWB 21-1 Issue I and AWB 35-1 Issue
1. Copies are enclosed for the Bureau's information.
CASA also notes that the Bureau has classified each of these
Recommendations as CLOSED-ACCEPTED.
In respect of Recommendation R20020109, CASA advises that it has
not yet
received responses to its invitations - the United States Federal
Aviation
Administration, the United Kingdom Civil Aviation Authority and the
European
JAA - to the liaise on the safety deficiencies identified in the
Brief.
Thank you for bringing this matter to the attention of the
Authority.
The following additional information dated 9 December 2002 was
received from CASA on 11 December 2002:
I am writing in relation to Recommendation R20020109 which arose
from Occurrence 200200095.
The Australian Transport Safety Bureau recommends that the Civil
Aviation Safety Authority liaise with the United States Federal
Aviation Administration, the United Kingdom Civil Aviation
Authority and the European JAA on the implementation strategies to
address these safety deficiencies.
In its responses, dated 29 August 2002 and 28 November 2002, the
Authority advised the Bureau that it had written to the relevant
bodies but had yet to receive a response.
The Federal Aviation Administration (FAA) has recently advised that
they had taken earlier action on the issues raised in the
Occurrence Brief, released on29 October 2002, and it appears that
they will not be taking further action. A copy of the FAA's
response, for the information of the Bureau, is enclosed.
CASA notes the comments at page 7 of the Occurrence Brief in
relation to the United Kingdom Civil Aviation Authority. That
Authority advised that "their research revealed, apart from the
example cited by the ATSB that complied, the only other UK built
aircraft to which these recommendations could apply was no longer
the responsibility of the UK CAA". Their production had moved to
the United States. Type certification responsibility now rested
with the FAA.
As notified earlier, CASA addressed the safety deficiencies, that
were set out in Recommendations R20020101 and R20020102, through
the issue of Airworthiness Bulletins AWB 21-1 and AWB 35-1.
On this basis, the Authority believes that there would be no
further benefit in pursuing the issue with the national bodies. The
Authority considers that it has now met the requirements of
Recommendation R20020109.
Thank you for bringing this matter to the attention of the
Authority.
