November 2012 - Indian Airforce

The time was 2100h and I had just finished my
dinner when my mobile rang. It was Gp Capt
xx C Eng B from the Command Headquarters.
He said that the VIP Avro ac of Command
Communication Flight had made an emergency
landing at Mumbai International Airport at 2030
h due to nose undercarriage red light remaining
‘ON’. Luckily there was no VIP on board and the ac
was returning to base. The ac had landed safely but
had been switched off on the taxi link due to nose
wheel steering failure and was being towed back to
the parking. The STO of the unit was on leave and
since I was the STO of the neighbouring AVRO unit,
I was asked to speak to the aircrew to ascertain the
complete snag and keep a rectification party ready
to go to Mumbai at first light.
I called the senior most aircrew who was a Sqn Ldr
with sufficient experience on type. He said that for
this sortie he was the co pilot and the captain was a Fg
Offr with about one year’s experience. He explained
that they had taxied out normally and after takeoff
when the undercarriage had been selected up, the
nose undercarriage light had changed from green
to red and remained ‘ON’, indicating that the nose
wheel had not locked up. They tried one cycling of
undercarriage and when the red light persisted, they
declared the emergency and carried out a priority
landing back at Mumbai. During the landing roll,
while turning onto the link, he (the Sqn Ldr) realised
that the nose wheel steering was ineffective and
therefore had switched off the ac after clearing the
runway. I spoke to one of my clueful Airframe Fitter
JWO and we suspected that the snag might have
been due to a bird hit during takeoff, which might
have damaged the nose undercarriage door linkage
and also severed the nose wheel steering cable.
However, it was reported by the crew that they could
not find any avian remains or damage, other than
two large dents on the right undercarriage door of
the nose wheel.
A rectification team with I as the team leader
(also the technical member of the Court of Inquiry)
was airlifted to Mumbai to ascertain the cause of
malfunction of the undercarriage and to undertake
rectification on site. Since Mumbai did not have the
requisite equipment, it was decided to carry even
the 10 ton jack along with other requisite tools.
Draining out of hydraulic fluid due to pipeline
rupture was initially suspected, however, it was seen
that the reservoir was still full and no abnormality
in the nose undercarriage system was found
during visual inspection. However two major dents
wherein one of them had torn the aluminium skin
were seen on the right front undercarriage door.
We decided to jack up the front wheel and do a
retraction test with pins on the two main wheels in
place. The system was energised and pressure built
up using the hand pump and the front wheel was
retracted. No fouling was observed and the nose
wheel undercarriage light changed from green to
red and upon getting locked up, the red light went
off. This confirmed that the system was working
perfectly well. The nose wheel steering was also
checked and tested thoroughly and was found to
be serviceable.
The team thereon proceeded to find the
cause of the dent on the undercarriage door.
The nose wheel toggle pin was removed and on
closer examination it was seen that the dent was
commensurate to the shape of the toggle pin
head and there were even traces of red paint near
the dent. The undercarriage was again retracted
this time with the toggle disconnected and the
pin fixed in the upper toggle. It was seen that the
undercarriage door got obstructed by the upper
toggle link at exactly the same place where it was
dented. It was therefore deduced that the ac had
taken off with the nose wheel toggle disconnected
and this had caused the nose undercarriage not
getting locked up and the red light remaining ‘ON’,
creating an emergency in air.
Exact Cause of Failure
Parking for AF aircraft in Mumbai is such, that it
requires being towed out of the slot during refuelling
or just before starting. In this case the ac was towed
out twice for refuelling and also just before departure
at around 1915h. During towing the nose wheel
toggle link is disconnected from the nose wheel
steering jack. However, in this case the ground crew
INDIAN AIR FORCE 2 0 1 2 N o v e m b e r Aerospace Safety 15