The failure of a link between different
systems at Swanwick air traffic control centre in Hampshire delayed
flights at major airports including Heathrow, Gatwick and Luton
yesterday, and hit some flights today.
National Air Traffic Services, which runs the Swanwick centre,
has apologised to travellers. Ian Hall, NATS' director of
operational performance, said, "Our systems are incredibly
resilient. We take every step to avoid any problems but are always
aware that in maintaining and updating highly complex systems, we
can experience difficulties." He said there was a backlog of
flights as a result of the problems.
When the link failed, NATS issued instructions for some flights
not to take off, which reduced the workload on air traffic
controllers who reverted to some manual processes to manage
aircraft.
The problem is understood to have been traced to a
communications sub-system between the IBM-based National Airspace
System, sometimes called the National Flight Data Processing
System, and Swanwick's separate, more modern area control
technology, which was built by NATS and Lockheed Martin. The
failure happened at 3.55pm. The full systems were back online by
7pm but some flight cancellations and disruption at airports have
continued until today because the sequencing of aircraft take-offs
had been disrupted.
There have been serious failures before of links between
Swanwick's systems and the National Airspace System [NAS] - but
this was the first of its kind. Engineers at NATS are still
investigating the exact cause.
The NAS runs on modern IBM hardware but parts of the software
date back decades. It is updated infrequently to keep it from
becoming unstable. The NAS software was due to have been replaced
in 2005 but this has not happened, mainly because NATS is
developing a new system with Spanish and German air traffic control
specialists.
Links between Swanwick's systems and the older NAS technology
are likely to be complex and purpose-built. NATS emphasises that
the failure was not of the NAS system itself.
The failure meant that air traffic controllers did not have the
information on their flight data strips updated automatically.
Although the correct information was in the NAS system, it was not
transferring to Swanwick's area control system. So updated flight
route information - including waypoint data - had to be input
manually directly into Swanwick's area control system.
The flight strips are used particularly when controllers receive
flights from other airspace sectors into their own areas. They were
able to see the position of aircraft on their screens from the
radar "blips". They also had historic text data on their screens of
the aircraft and its destination.
But flight strips are used by controllers, in part, to see new
or updated instructions which have been given to pilots. So
controllers know what aircraft are about to enter their airspace
sector and routing information. When the sub-system failed,
controllers lost the ability to have recent instructions to pilots
updated automatically. When the information had to be handled
manually, this reduced the number of flights controllers could
manage.
Hall said yesterday: "Safety has not been compromised at any
stage and we sincerely apologise to those who have been
inconvenienced this evening. We are working closely with airlines
to increase capacity this evening to help minimise delays and
impact on the rest of today's schedules."
Controllers reported no particular difficulties in reverting to
some manual procedures. But airlines reported scores of delayed or
cancelled flights and some passengers missed flights because of
long queues at check-in desks. British Airways said the further
cancellations on Friday affected only short-haul flights. They were
the result of a knock-on effect of 35 cancelled domestic and
European flights on Thursday, said BA.