Aircraft put under the control of other centres as Swanwick
struggles to cope, despite new £337m systems
National Air Traffic Services (Nats) is asking some aircraft to
avoid the £623m Swanwick air traffic centre by flying at lower
levels to come under the control of the ageing West Drayton centre
near Heathrow.
The Swanwick New En Route Centre near Fareham, Hampshire, went live
in January at a cost of £623m - more than half of which was for new
computer systems - so that it could take over from the West Drayton
area control centre and bring an immediate 40% increase in
capacity.
But a shortage of controllers at Swanwick has caused record delays
for airlines this year, despite traffic levels being down after the
11 September terror attacks.
To help to overcome the shortage, which is expected to last through
this Christmas and into next summer's busy period, Nats is
transferring "area control" of some flights over 20,000 feet, that
would normally be handled by Swanwick, to lower altitudes where
they can be handled by "terminal control" at West Drayton.
But a leaked internal Nats notice alludes to a possible safety risk
if aircraft are "height-capped" because too many faster jets could
be transferred into a lower airspace normally occupied by
slower-moving business and propeller aircraft.
"The impact of height-capping jet flights at [20,000 feet] or below
can dramatically affect the complexity of a sector," warns the
notice.
The height-capping reduces flight delays because terminal control
at West Drayton is able to handle some of Swanwick's traffic. But
it raises doubts about whether Nats can justify the £337m cost of
Swanwick's systems when some of the new centre's work is being
systematically transferred to West Drayton and other control
centres.
An extension to earlier trial height-capping procedures by Nats is
described in an internal Temporary Operating Instruction dated 23
November.
"These height-capping procedures are intended to move specific
demand from the upper to lower airspace as a result of excess
demand," says the notice.
It adds that managers "are to consider" height-capping flights in
certain circumstances where delays of 20 minutes or more are
expected.
As some airlines are "likely" in advance to lodge flight plans that
specifically avoid Swanwick, the notice warns that height capping
may have to be regulated, or delays could be shifted from Swanwick
to other air traffic control sites.
Height-capping will incur a fuel penalty because jets use more fuel
in the denser air of lower altitudes, and it could also have
adverse environmental effects because jet engines are more
efficient at higher altitudes.
Nats said this week that height-capping was an old technique that
was applied routinely before Swanwick went live.
Staff, however, say that height-capping was used at West Drayton
only in specific, tactical circumstances but is now being applied
much more widely to exclude as much air traffic as possible from
Swanwick.
A Nats spokesman insisted that height-capping was not solely in
response to a shortage of controllers. "The [height-capping]
service has proved to be beneficial to airlines not only in
avoiding air traffic control delays but in assisting them to
maintain schedules that have been disrupted for other reasons such
as operational delays, poor weather, etc".
Nats added that pilots are height-capped more than in the summer.
Its staff point out that air traffic is currently at generally
lower levels than the summer.
Pilots' voice messages get cut off
A leaked internal
Nats notice dated 12 December says that some pilots are having
their voice messages to controllers cut off after two seconds,
which is regarded as a possible safety-critical issue. "To date
investigations have not been able to replicate the fault or locate
its precise cause. The issue has a high priority and further
investigation is being carried out to locate the source of the
problem," says the notice.
A Nats spokesman would not comment on claims that pilots may
continue talking without realising at first that they have been cut
off.
The problem of "truncated transmissions" had happened on only a
"handful of occasions in 1.5 million flights handled this year.
Safety had not been compromised", said the spokesman.