| One Thousand To Level
(Bust?)
by Tim Atkinson
What is a level bust? A level bust occurs
when an aircraft deviates (climbs or descends) more than 300ft from
the correct level. Normally vertical separation between aircraft is
1000ft.
One Thousand to Level (Bust?)
Have you had a level bust? If you haven’t, then
you have probably flown with someone who has. What do you think about
the consequences of a level bust? A quick reaction to TCAS, some
paperwork, maybe a ‘chat’ with the Senior Pilot…. A few weeks will go
by and the event will drift into insignificance…
 On
November 11th 1996, a Boeing 747 collided with an Ilyushin 76 west of
New Delhi. 349 people were killed. The accident was the result of a
simple level bust. You might be forgiven for thinking that a similar
accident couldn’t occur in Europe. With a modern radar system, high
quality Air Traffic Control, and TCAS, many would have agreed with
you. The events of July 1st this year (2002) should have changed your
mind.
On this date, a Tupolev 154 collided with a
Boeing 757 near Ueberlingen, Germany. This accident happened in
well-regulated European airspace with a high-quality ATC service, and
involved aircraft equipped with TCAS flying in VMC. Whilst this event
was not a level bust, it demonstrated that the ‘error traps’ or
‘safety nets’, which should prevent a mid-air collision, cannot be
relied upon to work.
This should remove any doubt from your mind as
to whether level busts are a serious safety hazard. Are they a greater
hazard than they were? Probably, yes. GPS-based navigation systems
mean that aircraft track airway centrelines and departure and arrival
routes with pinpoint accuracy. In the past, inaccuracies in tracking
meant that there was a good chance that aircraft on similar tracks
would miss each other. Now, if two aircraft are on a theoretical
collision course, they’re probably going to meet. RVSM, with its
requirements for greater accuracy in vertical navigation, has a
similar effect. It also means that if something does go wrong, there
may be much less time and space in which to react.
Work is being done in many areas of industry to
ascertain why level busts occur and to define preventative measures,
but it is clear at this stage that pilots can adopt operating
methods which will substantially reduce their risk.
Shopping for a level bust? Take this list…
The vast majority of level busts are caused by
one or more of the following factors:
1. Deviation from SOPs
2. Mis-reading SID charts
3. Altimeter setting errors
4. Callsign confusion
5. High workload not mitigated
6. Confusion between heading and level
instructions
7. Aircraft cleared FL110, but descends to
FL100
8. Confusion or misunderstanding not
checked with ATC
9. Autopilot failure to capture level
So, the problem has been analysed, and is to
some degree understood. However, none of the causes above has a simple
and robust cure. The information above does give us the opportunity to
find ways of adapting our operating techniques in order to reduce our
exposure to risk.
Positive change…
We need to pay attention to SOPs, RTF
procedures, and the flight deck environment. Whilst the following
advice may seem elementary, we need to think carefully about each
point, and amend our own operating styles accordingly… The training
department and audit team will be concentrating on these issues in an
effort to ensure that standards are improving.
What’s it he doing now?
The importance of understanding and abiding by
company SOPs cannot be over-emphasised. This sets the scene for a safe
operation, and engenders high quality co-operation between
crewmembers. Each understands what to expect and recognises the
professional manner in which the other sets about their work. This is
an environment in which mis-understandings and confusion are not
likely to flourish. Achieving this goal is not straightforward, only a
disciplined individual approach will produce a high standard of
adherence to SOPs, and this should have its roots in an understanding
of the need for a standardised operation.
 SOPs cover the way that we set the aircraft up
for flight, especially the departure phase. Approximately 35% of all
level busts involved pilots mis-reading the departure chart, and
expert opinion is that users of Jeppesen charts are most at risk. It
is vital that we take time to read, understand, and brief the
departure plate accurately, and then manage the aircraft flight path
in order to achieve the correct profile. Particular attention needs to
be paid to ‘Step Climb’ SIDs, which have a far higher rate of level
busts than others. One good technique is to carry out the departure
brief and ask an open question of the other pilot, ‘What is our first
cleared altitude?’. This interactive style of briefing ensures that
both pilots have a clear comprehension of the profile.
Altimeter setting errors, usually involving
failure to set Standard Pressure when first climbing to a Flight
Level, also account for a substantial proportion of level busts. A
clear brief, and careful SOP adherence, should help you to avoid this
error. The –700 series aircraft will give a warning if climb is
continued above Transition Altitude without STD being set, but this
error trap is absent on the –300. Talks are ongoing with Smiths and
Honeywell to seek a technical solution.
Some difficulties with autopilots have been
cited in level bust reports, generally where crews have attempted to
engage the autopilot too late during a level-off. The usual advice
applies, hand-fly only where appropriate and following a brief. Use of
the ‘Manual Veto’ may be helpful – this allows either pilot to call
for the autopilot if the workload is felt to be too high.
These techniques ensure shared understanding,
and will help to avoid one of the most statistically risky types of
level bust.
That must have been for us…
We operate modern aircraft – some only a few
weeks old – and the air traffic control systems in many parts of
Europe are up-to-date, too. Connecting the aircraft to the controller
though, is a system which has been proven time and time again to be
unreliable and awkward. Voice communications by VHF allow for all
sorts of errors.
Operating professionally means taking care to
communicate effectively, and this means setting up the receiver
correctly, listening accurately and taking care to respond only to the
correct callsign, and being aware of the traffic environment from
other communications. When transmitting, it is vital to listen out
before calling on a new frequency, to use standard words and phrases,
and to seek clarification if there is any question at all over the
communication received. At least one pilot must monitor VHF1 at all
times – many prefer, when listening to ATIS broadcasts, for example,
to leave VHF1 selected and audible, and to pick up the ATIS quietly in
the background. Put simply, VHF radio is not your friend – it has the
potential to do great harm, and needs to be used with utmost respect.
It is vital that readbacks are not used as a
means of seeking clarification – this is not their purpose. Callsigns
should never be abbreviated, and words such as ‘flight level’ and
‘heading’ should not be omitted from readbacks. If you think the
standard of the communication from the controller is poor, seek
clarification.
All of the above is achievable, though it will
require determined effort, especially on a demanding multi-sector day!
One significant way in which safety may be improved is by eliminating
distraction in the flight deck, certainly in climb and descent, and
when approaching the point at which descent clearance may be received.
This means concentrating on the old priority list – ‘aviate, navigate,
and communicate’, and not allowing choosing from the breakfast menu to
get in the way of any of these tasks.
Malaga, this is Easy Seven Victor Tango Four
Alpha Bravo…
Callsign Confusion has been identified as a
contributory factor in all sorts of incidents, and a programme is
underway to alter all of our callsigns, taking account of Go’s
operation too. This is a major project, and will not happen overnight.
The objective is to find a satisfactory solution for the long term,
and in the meantime, extra vigilance is necessary whilst using our
present callsign scheme.
Missing You Already!
The techniques above will help us to avoid level
busts – but we may still be involved in an encounter with another
aircraft. The accident on July 1st 2002 should prompt us to reconsider
collision avoidance, and the following are food for thought. Keeping a
good lookout, weather permitting, provides a last line of defence.
Normally, TCAS will inform us of traffic in time to commence a visual
search. There is some opinion that pilots have become conditioned not
to react to a collision risk until TCAS activates. In fact, if a
definite and immediate risk of collision is identified, the crew
should take action to alter the flight path. Of course, any TCAS RA
should be followed, but a timely and gentle manoeuvre will, perhaps,
avoid an RA, too. What appears to be a dangerous situation may be
queried with ATC, (who may be very grateful for a prompt!).
So that’s all?
Taking care to abide by these guidelines will
have a very substantial effect on our exposure to risk. In recent
level busts and AIRPROXes, which have happened to easyJet crews, one
or more of these guidelines were broken. We can’t afford exposure to
unnecessary risk – we have to adapt and improve.
The controller’s ‘bible’, the Manual of Air
Traffic Services Part One, gives a full account of standard RTF
phraseology as used in the UK. Other European states use slightly
different phraseology. The Manual is available online
here,
and Appendix E is the appropriate section.
The UK AIP also gives
relevant information
here
(You will have to register - free).
CAP413 gives an overview of RTF techniques
here.
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