Note of visit to British Airways Maintenance,
1. To provide a context for the technical evidence
that would be received during the Inquiry, a party from the Sub-Committee
visited British Airways Maintenance, Cardiff (BAMC) on 13 April
2. The visiting party consisted of Baroness Wilcox
(Chairman of the Sub-Committee), Lord Flowers, Lord Jenkin of
Roding and Lord McColl of Dulwich, supported by the Sub-Committee's
Specialist Adviser (Dr D Michael Davies) and Clerk (Mr Roger Morgan).
3. The visiting party was welcomed to BAMC by
the General Manager, Mr Bruce Hunter. He explained that BAMC serviced
aircraft for a number of airlines, including British Airways (of
which it was a wholly-owned subsidiary) under broadly similar
contractual arrangements with the operators.
4. Mr Marc White, Technical
Services Group Leader, briefed the visiting party on the ventilation
arrangements of a Boeing 747-400, the main elements of which were
(a) On the ground, cabin air was provided
by a bleed from the compressor stage of an auxiliary power unit
(APU) in the tail. The APU also provided power for the air conditioning
although, for very hot locations, air conditioning could be supplemented
by locally supplied external units.
(b) At cruising height, the external air was
both too cold and at too low a pressure to be used without treatment.
It was compressed in the compression stage of the turbines feeding
the jet engines. By compression alone, the air was heated to some
(c) This compressed air was ducted to the air
conditioning bay between the wings at the bottom of the fuselage.
Here, most of it was cooled by external air passing over heat
exchanger fins and further, as necessary, by a refrigeration unit.
The pressurised and cooled air was then spun through a vortex
to remove any condensed water.
(d) Suitable pressure was maintained in the cabin
by balancing the rate at which air was supplied and vented away.
Air from the galleys and toilet cubicles was expelled immediately.
Of the remainder, half was allowed to bleed away and half was
filtered through high efficiency particulate air (HEPA) filters,
as used in hospitals, and mixed with the newly conditioned air
for distribution to the various zones in the aircraft cabin. This
re-circulation helped boost humidity of the very dry external
air to about half the levels normally experienced on the ground
in the United Kingdom.
(e) The same air was supplied to all zones. The
only difference between zones was that the temperature could be
controlled individually by the crew. This was done by altering
the amount of hot pressurised air fed direct into the circulated
(f) The air was injected along each outside edge
of the cabin ceiling, and extracted along each edge of the cabin
floor. Vents directed the air to across the top half of the cabin
to the centre. It was then drawn back across the bottom half of
the cabin to extractor ducts at floor level. The vents were designed
to minimise flow along the cabin.
(g) The whole volume
of air was exchanged every two or three minutes. As noted, half
the replacement was re-circulated air so, while enough fresh air
was drawn in to replace the cabin air completely every five minutes
or so, the actual replacement was a form of progressive dilution.
(h) Increasingly, aircraft did not have individual
air nozzles for each passenger. Where fitted, these supplied the
same air as otherwise available, but the air felt cooler because
of the concentrated movement.
(i) All air controls were managed from the flight
deck. Normally, this was done automatically although manual control
was possible, as might be required in an emergency. For example,
it might be desired to flush the cabin with fresh air. Alternatively,
the supply of fresh air could be shut off if it were tainted -
in which case, oxygen could be supplied to passengers through
5. Mr White also briefly outlined the ventilation
arrangements on the newer Boeing 777. These were very similar
to the 747 except that incoming air was treated to remove ozone;
only fresh air was fed to the flight deck; re-circulated cabin
air was passed over an anti-fungal felt; and, by design, there
were differences in some of the service intervals.
6. The visiting party then visited a stripped-down
Boeing 747-400 to inspect its systems at first-hand. During this
and subsequent discussion, the following points were noted.
(a) The HEPA filter-packs seemed very robust,
allowing minimal chance of failure. Even so, it appeared that
there was no check for any failure during the two year service
life. (However, an alarm would sound if a filter were blocked.)
Nor were any routine tests made of filters after replacement to
assess the job they had done.
(b) New filters did not reach peak efficiency
until they had been used for a while. However, there were no arrangements
for pre-treating filters before installation.
(c) Both the maintenance arrangements and qualifications
of maintenance personnel were tightly controlled by the regulatory
authorities. While part of the maintenance arrangements relied
on self-certification, this was covered by strong audit and reporting
arrangements that should minimise the possibility of any shortcuts
in quality control.
7. On departure, the Chairman thanked Mr Hunter,
Mr White and their colleagues for a most useful and well-arranged