What follows is some of theevidence given by Squadron Leader Robert Burke
to the House of Lords committee which investigated thecrash of Chinook ZD576 on the Mull of Kintyre.
Burke gave evidence to the Lords' committee on 16 October
2001.
Burke had been unit test pilot at RAF Odiham in North Hampshire,
which is the home of Chinook helicopters.
He referred to Boscombe Down which is where the
Fadec software for the Chinook Mk2 - the type of helicopter
which crashed on the Mull of Kintyre - was tested. Boscombe Down's
IT specialists were so concerned about the
Chinook Mk2 software that they had recommended a rewrite - but
this did not happen before the aircraft went into operational
service. Soon after Chinook ZD576 went into service with the new
Fadec system it crashed and the
pilots were blamed.
House of Lords committee, questioning Squadron Leader
Robert Burke: Do you know the circumstances in which the pilots at
Boscombe Down had refused to fly a Chinook Mark II?
Burke: I can only talk about basically what I
know, and I heard Squadron Leader Morgan's comments on it yesterday
I was here. My perception was somewhat different because I was
talking to Boscombe Down, just like the OCU were, not on a daily
basis, but on a reasonably regular basis as part of my job as the
unit test pilot at Odiham. It was part of my terms of reference to
keep contact with other test organisations, which I did both here
and with Boeing quite a lot. My very strong perception,
particularly when talking to the senior man in the Chinook project
team, the American major, was they were very unhappy with the
Fadec[Full Authority Digital Engine Control] system generally,
extremely unhappy, because they had had a lot of problems,
particularly on the ground, with the engines running up and running
down. Whether they refused to fly it or not I can only comment on
the following, the atmosphere between Boscombe Down and RAF Odiham
was very strained indeed, especially after the accident-it was
pretty strained beforehand because of restrictions on the aircraft
and one or two other things. It got to such a point that Boscombe
Down sent a project team up to Odiham and briefed the executives at
Odiham the station commander and senior engineering officers,
flight commanders and myself. They made a formal presentation at
Odiham on the problems they had been having at Boscombe Down. It
lasted about an hour and a half. When the meeting ended the
atmosphere was even less amicable than when it began. There was no
doubt in my mind, I cannot speak for others, well I can to a
certain extent because we discussed it when we came out of the
meeting, that Boscombe Down's air crew were not prepared to fly the
Chinook or continue flying it because of problems with the Fadec,
they were not happy with the reliability of the system. I can also
say that I personally had to fly the Boscombe Down aircraft back to
Odiham for a minor servicing, me and an Odiham crew, because the
Boscombe Down crew would not fly it. To fly this particular
aircraft, because of paperwork considerations, the aircraft was
assigned to MOD (PE) at Boscombe Down, not the RAF, so it was their
aircraft. It was also fitted with quite a lot of non-standard test
equipment, so it had modifications. For me to fly it back a
"service deviation" or a series of them had to be issued to allow
me as an RAF pilot, not a Boscombe pilot, to fly it back and for me
to fly the aircraft with these various modifications. I suggested
many times that it would be much easier if Boscombe flew the 12
minutes back to Odiham and they would not do so. I spoke to the
pilots and they would not do so. I then asked the pilots if they
were prepared to meet me at Boscombe Down and discuss the
implications of these modifications and they would not appear, they
would not do that. So my perception of whether Boscombe would fly
or not was very different, perhaps, to that received by Squadron
Morgan in his one telephone call. I was quite interested to know
when he said Boscombe rang up the next day after the crash and said
it was basically nothing to do with why they stopped flying. How
they knew what was wrong at Boscombe Down I have no idea,
considering we are still discussing it some seven years later. I
believe a number of people have also drawn your attention to a
document which was a draft DO (Demi Official Letter) from the
AOCinC to the ACAS about Chinook flying, which has apparently had
fairly wide circulation. I am not sure how. You have a copy of it
so you are able to read the first paragraph, "it is, a) announced
for the second time this year because of their concerns about
safety of the Fadec system they had stopped trials flying the
Chinook Mark II". It could not be much clearer than that, it was
from a very senior airman. It goes on to say, "we are all agreed",
this is Boeing and ourselves, the RAF, the frontline squadrons,
"the Chinook Mark II is safe to operate and there can be no excuse
for AAEE not to fly at least to these parameters". That was pretty
well the view of most of the frontline pilots in the RAF at the
time in the Chinook force.
Lord Tombs: Are the Boscombe Down pilots civilian or
service pilots?
Burke: They were service pilots at that time,
one was an American officer on exchange and the other one, who I
have spoken to since then, is retired working in the City now. The
project leader was an American Army pilot on exchange, he may have
been an American Air Force pilot, Major Myers.
Lord Hooson: Did you gather that the sense of unease was
due to their own experience or general gossip in the
Mess?
Burke: I can go into that in some detail, my
Lord, the Boscombe Down one, and people knew what was going on at
Boscombe Down, was because they had unexplained run ups and run
downs and things. At RAF Odiham we had a series of problems with
the Chinook Mark II, particularly concerning Fadec. I can only go
into these quite specifically, one was dealt with at considerable
length yesterday, the testing for the overspeed system. One of the
concerns of any helicopter pilot is that the rotor will overspeed
to the point where it will be seriously overstressed and fly off. I
make that statement quite categorically. That is a major problem.
Any rotor if you overspeed it and overstress it is likely to fly
off. All helicopter pilots are aware of that. The designers of
Fadec were equally aware of that and incorporated a last ditch
system, basically that if the rotor speed got to 114 per cent, or
something like that, this system cut in and stopped any more fuel
flowing to the engine. This overspeed trip was probably the system
which gave us the most problem of all when we were testing it on
the ground. Boscombe insisted we had to test it before every flight
because they said, "we are not very confident in Fadec, you have to
test this before every flight". This test procedure led to a number
of run ups and run downs. Pilots did not like doing it because you
had to watch the engine like a hawk in case they over-temped or ran
away. You heard a great deal about it yesterday. There were a
number of other concerns, so many in fact that the squadrons-I
cannot talk for all of the squadrons but I can talk for 7 Squadron,
which was the resident operational squadron at Odiham, produced
their own local orders, I will not say to bypass certain
procedures, but because we were getting so many fault codes on the
Fadec. Like any computer the Fadec system was subject to
malfunctions when it had power interrupts. Because of the way,
excuse me for going slightly technical, but it is necessary to
explain this, the generators and the standby generator were
arranged on the Chinook when you closed down and the standby
generator came on there was a power interrupt on the system. It has
probably been cured by now. The Fadec DECU, the Digital Electronic
Control Units, had number codes on them and if it came up with 88
all was clear, the system was fine, but very often on shutdown,
because of electrical interrupts, we came up with a whole variety
of codes which meant technically you could not fly the aircraft
until the technicians had a serious look at it that is what was
laid down. One of the local orders was that if the aircrew got any
codes other than 88 we were technically not allowed to fly,
squadron ground crew would come out, pull two circuit breakers,
push them back in again and hoped that cleared the faults. It was
not a recognised procedure but the squadrons would use that. That
did not lead to confidence! There was also a mechanical fault in
one of the multi-point connectors that went from the engines into
the DECU, basically the electronic computers. The multi point
connector was not of a good design, again you had power interrupts
on the system. The squadrons introduced a procedure, probably the
OCU did as well, but I am not certain on that point, where the
crewmen every quarter of an hour would have to go up and check
physically that this multi-point connector was not vibrating
loose.
Could any of these defects that you heard about or
experienced-
Burke: I experienced them as well
-could they have resulted in a loss of control, even
temporarily?
Burke: If you have a power interruption to the computer,
certainly. There were various safety systems built in but the Fadec
is a computer like any other computer. It had a back-up system
which was very largely independent but it did not always work and
there were certainly recorded instances, I can give you the name of
the pilot but I cannot recall the aircraft, I think there were two
or three of them from memory, but I cannot be certain, when due to
possible power interrupts the pilots lost control of what are
called the engine condition levers, which were not throttles but
performed something like a throttle. You had three positions to
stop, ground idle on the ground and full power and you could lose
control of those and disable them due to certain electronic
problems. This certainly happened. I can give you the name of one
of the pilots involved in that.
**
Burke (an explanation of how Fadec words): The
engine condition levers are three-position levers up there at the
cockpit and one position is a stop position, one is in ground idle
position, where you set the aircraft rotors running on the ground,
and one is full throttle. The full throttle is then modified by the
Fadec or on the old Chinook by a purely hydro mechanical system to
bleed off from full power. The engine is set at full power and it
is bled off and whatever kind of computer or fuel control system
you are using, adjusts the power of the engines to keep 100 per
cent rotor speed. The engine condition levers take you from these
particular conditions, stop, ground idle, then full throttle but
that is modified by the fuel control system, the Fadec in the case
of the Mark II, in response to the rotor speed and how much power
you are using. This is the collective or thrust lever.
Is there anything in the over-temperaturing of the
engine by the Fadec system? You refer to this but does it produce
any serious results at the time? When the engines are over-temped?
You said that several engines had been
over-temperatured.
Burke: The Ministry of Defence will give you
better information on this than me, but I have seen two or three
engines which have been over-temped. You have to scrap or
completely rebuild the back end, the hot end of the engine.
If they become over-temperatured in flight is that
likely to have a serious result?
Burke: Yes it is likely to have a serious
effect on any jet engine. In fact, because we have engines which
are split into two halves, the front half produces a lot of gas
going at high speed and that drives another turbine at the back
which is connected to the rotors. There is a loss of engine drive
to the rotors as well almost straightaway, especially if the things
melt or start getting distorted.
You have commented on torque mismatch. Is that when a
differential power is produced by each engine?
Burke: Yes. One of the functions of the Fadec
(and you will find it in my layman's guide to the Fadec) is to
match the power between the two engines so they are sharing the
power to the rotors. If you get a mismatch of torque it means that
one engine is doing no work and the other engine is doing all the
work. There might be a good reason for that. One engine may have
lost power, malfunctioned or, in the case of a runaway, it might
well be producing too much power.
What is the practical effect on the aircraft of a
significant torque mismatch?
Burke: It all depends whether you are in a
benign flight regime or if you are very heavy. Perhaps the one
engine that has gone up might well then have reached its limit and
it cannot produce any more power or it might go into emergency
power or something like that. In a benign flight regime it has
really very little effect.
I think you mentioned that large numbers of the Digital
Electronic Control Units were returned to the makers for fault
investigation, is that right?
Burke: Yes, I think it has happened again
since. Because I was the unit test pilot involved in maintenance I
can remember that we had run out of DECUs, all of the aircraft in
the hanger, the ones undergoing overhaul, had been robbed of their
DECUs and at some stage the frontline aircraft could not get up to
sufficient numbers because we had run out of DECUs. The situation
was very bad, this is from personal memory, there were many days at
Odiham when we only had one Chinook available for training, some
days when we had none, and the situation got so bad, as far as my
memory serves me, when, the final straw was another DECU going down
and we had no aircraft available and the Northern Ireland standby
aircraft had to be used for the United Kingdom standby
commitments.
What was the position, was this a design
problem?
Burke: Nobody really knows, my Lord, because on
most of the ones that went back no fault was found. All the ones
that were taken out had something going wrong with them, that is
why they were taken out. Part of the problem was that because of
the speed at which this aircraft was introduced, the ground
technicians were not terribly familiar with the systems and what
they did was take out an unserviceable DECU and sometimes swap them
across from side to side and, as with any bit of electronic
equipment, as soon as you start moving it round the connections
start going and you will find that most of the problems on any
computer are probably simple electrical connections and the more
you move them the more problems you get. I do not know whether the
problems persist in that area, and I cannot answer that, but at the
time we were desperately short.
**
You mentioned in the aircraft which crashed there had
been Fadec related incidents on 16, 17 and 19 May 1994, could you
expand on that a little, please?
Burke: Offhand I would rather not. The details
are already available in the documents. My memory would not be as
good as the documents.
You refer to there being primary channel and
reversionary system, is that in relation to the Fadec?
Burke: Yes, my Lord.
Are they completely independent of one another or is
there an extent to which they run in series rather than in
parallel?
Burke: There is at least one area in the
shutdown procedures where they run in series. I believe there are
others but I am not the best person to answer this, there is an
expert on the subject, Mr Malcolm Perks, whose name you may have
seen, and I would much rather you ask him that question. It is four
and a half years, or rather less, since I used the system and I
would rather not comment on that detail.
**
You then refer to a possibility of engine malfunction,
four kinds.
Burke: Yes. Would you like me to read it out? I
have looked at this again and I have not really got anything to add
to it. There might have been a run away up, a run down, an engine
freeze or the RPM cycling up and down. All of those can occur in
any fuel control system. The engine freeze is unlikely to have any
operational effect. The run down is likely to have the aircraft
descending and slowing down probably very rapidly.
You exclude that?
Burke: I think it unlikely, I do not exclude
them, I think they are very unlikely. On the other hand if there
had been a temporary run away up or partial run away up, or RPM
cycling up and down the aircraft would have entered cloud, for
reasons I will go into. A temporary increase in the rotor speed
could have occurred even though the other engine had backed off as
quickly as it could, when one goes up the other one will try to run
down as fast as it can. How fast it runs down is, to a certain
extent, limited by the various controls in the system. The one that
is running up, of necessity something is wrong with it for it to
run up and it might run up jolly fast. This will start the aircraft
climbing, the lift coming from the increased rotor speed, the
faster the rotor goes round you will get an increase in lift. That
is not what we use to increase our lift but that will happen. The
pilot fearing total run up will have raised the collective lever to
contain the rotor RPM, this is an essential drill towards a first
action in the simulator. Although there are flip cards, you have to
know some of the drills, they are immediate actions. If you look at
the flip cards at the time, it may differ now, for a run away up
you will not find it there. This is taught as an immediate and
instinctive reaction to the flight simulator in Farnborough, as it
was then, and by raising the collective lever you increase the
pitch on the blades, the lift on all of the six blades increases
the lift at the same time, so you are in cloud.
That means that the blades offer more resistance in the
air as they go round?
Burke: They do. You increase the drag, that is
the immediate way of slowing the rotor down. I will read this out,
if I may, I do not want to change what I wrote three years ago,
"the handling pilot by now would clearly unexpectedly be in cloud
and have had to transfer to flight instruments having had his
vision outside the cockpit, peering through the windscreen. . .",
looking ahead, "the collective lever would have been well up under
his left arm, he would yank the collective lever up until the rotor
speed was contained. The engine instruments and the flight
instruments would have been very difficult to read because of acute
vibration". This is something which cannot be simulated and can
only be experienced. "Even that is nothing like the vibration which
appears to be higher with high power on". I will talk about
self-tuning vibration absorbers. These are massive absorbers,
basically levers on springs under the pilots' seats and the
instrument panel and these are there to absorb the naturally large
vibration experienced particularly in tandem rotor helicopters.
You say the aircraft would be yawing
severely?
Burke: It might have been yawing, it might have
been doing several things, but yawing particularly because the
pilots would have kept the aircraft straight and level. The rotor
speed at this stage would be going up and down. The rotors are not
flat on the top, they are like that (indicates) at an angle to one
another.
When you say "yawing" it would be going from side to
side?
Burke: Sliding like sideslip in a car or
skidding in a car.
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