By Shyam Hattangdi
There was never a dull moment in Gnats that I had an opportunity to fly, off
and on, from 1965 to 1982 and I had my share of incidents in ample measure.
One particular incident is worth mentioning.
It was a routine air test on a bright clear day and as I was climbing
through about 22,000 feet, I felt a slight “click” on the control column and
the aircraft began to gently roll to one side. This was easily controllable
and there was no indication of any other problem and the hydraulic pressure
and cycling were within normal limits. However since the problem involved
flight controls I decided to discontinue the air test and return, informing
ATC accordingly. Passing about 20,000 feet I decided that it would be wise
to get the wheels down as soon as possible as it could be an impending
hydraulic failure and, informing ATC of my intentions, reduced speed and
selected the undercarriage down.
At the time it was not very well known that a single aileron reverting to
manual could lead to a violent roll with the undercarriage down, and as the
gear came down all hell broke loose. The stick was snatched out of my hands
and the aircraft began to roll violently and pitch down completely out of
control. The stick was jammed to the extreme left and I was unable to move
it laterally even with both hands and all my strength. I felt that there was
no time to even attempt an R/T call and that ejection was the only option as
I was losing height rapidly. Since the violent behaviour was like a spin, I
thought to myself that I must jettison the canopy before ejecting. This
rationalising seems to have helped me regain a little of my composure after
the initial shock. When I looked down to locate the canopy jettison handle,
it occurred to me that my last action had been lowering the landing gear and
the erratic behaviour had started as the gear had come down. Since I still
had about 4000 feet in height before a mandatory ejection, as a last resort,
I decided that I should try raising the landing gear to see if that was
indeed the cause. Sure enough, as the landing gear came up, the aircraft
became controllable and I was able to level off though the slight roll to
the left still persisted.
ATC was informed and, late Air Marshal Gole, who was then a Wing Commander and commanding the other Gnat squadron on base and, if I remember right, officiating as Station Commander, rushed to the ATC and took charge. Then on matters proceeded systematically. I had plenty of fuel and so there was no great urgency. He gathered a team of experts and the discussions, opinions, and suggested actions were all recorded, I was told later. This left me free to concentrate on flying.
I was then told to see if the problem persists if hydraulics were switched
off. After switching off hydraulics and exhausting the residual pressure, it
could not be ascertained if the pressure was fully exhausted as the usual
“click” on the controls was unidentifiable even after attempting to exhaust
hydraulic pressure for a long time. Moreover the slight roll to the left
continued to persist. Lowering the undercarriage on manual would probably be
possible but it would rule out the option of raising it again and if the
uncontrollability persisted, ejection would be the only alternative left,
and that too under awkward conditions. Later attempts to lower the gear in
power were made but had to be quickly abandoned as the aircraft would begin
to go out of control as the ailerons started to droop.
After much discussion on the ground, it was finally decided to ask me to
eject. A belly landing was not suggested as there was no precedence and the
safety of attempting it was rather uncertain because of a weak floor, low
seating and the anhedral that may lead to cart-wheeling if a wingtip should
However since I felt confident of carrying out a belly landing and it would
also make it easier to identify the cause of the strange behaviour, the
decision to opt for a belly landing was left to me. Slow speed handling
appeared to be slightly worse with the gear in airbrake position and so I
elected to attempt a fully wheels up belly landing.
There were two fire tenders available and so it was decided that one will be
used to lay foam on the runway and the other reserved for firefighting after
landing. Accordingly about 300 feet of the runway was sprayed with foam and
I burnt all the fuel on board in preparation for a belly landing.
The approach was uneventful and I was able to simultaneously switch off the
engine and put the aircraft down where the foam carpet began. The noise
level of the metal scraping the runway was very high and it was like having
my head in a bucket. Since the small rudder was the only means of
directional control it was like controlling a car with a couple of full
circles of steering “play” and it took all my effort to keep the aircraft on
the runway with the nose pointed in the right direction, though I did manage
to finally stop on the centerline. Every time the nose swung, there was
also the associated roll that had to be controlled as there was the
possibility that a drop tank may separate and the aircraft may cartwheel.
I had disconnected the R/T cord in preparation for a quick get away as I
came to a stop and so could not hear the ATC who was apparently yelling for
me to get out as the residual fuel in the drop-tanks had ignited when the
aircraft left the foam area. When the aircraft came to a stop thinking that
everything was fine I began to get out of the cockpit. It was then that I
looked back and found the aircraft on fire. The fire tender was there as I
was getting out and sprayed everything, including me, with foam. I ran to
the side of the runway only to find a “rescue” MI4 helicopter bearing down
unusually fast. It landed with a thump, bounced and landed again a few feet
further – apparently there was much excitement all around!
As Adi Ghandhi has pointed out, the stink of the foam did not leave me for a
quite a while and the members of the COI had to hold their noses while
conducting it. Fortunately they were able to ascertain the cause as an
aileron filter blockage that was subsequently rectified by a design change
(coarser filters, balance pipes etc. if I remember right) and the “V” check
was introduced prior to taxi out to physically check if the ailerons go into
manual simultaneously when hydraulics are shut or fail. Procedures to check
that both ailerons were in power prior to line up were also put in place.
With hindsight, it may have perhaps been possible to get into manual, lower
the wheels on emergency and land normally but the occasion demanded actions based on a dynamic situation and the knowledge available at that point in time and a more methodical approach could not have been taken by Air Marshal Gole and the rest of those on the ground. Moreover, the event helped to positively identify a problem that may have been the cause of numerous accidents, some fatal, in the past. Luck of course played a big part as it usually does – had I waited to lower the landing gear on downwind instead of at height, the outcome could have been quite different.