[Naijanet] Report cites faulty bolt as cause of plane crash
Fabiyi, Kolawole A (KAFA)
By Sola Dixon, Aviation Reporter
Guardian; 9 Feb 2000
POOR maintenance culture and a bid to protect commercial gains caused the
1998 crash of a Bristow helicopter in which five people, including the pilot
died at Onne, Rivers State, according to the report of an investigation into
the accident.
The company's maintenance personnel had during an earlier inspection of the
aircraft, noted a defective bolt but opted to defer its replacement to a
later date, the report added.
The 21-page "Civil Aviation Accident Report No 04/366" which was presented
to Aviation Minister, Dr. Segun Agagu last August, was officially released
recently.
Registered as 5N-AJL Bell 212, the aircraft was allowed to embark on the
ill-fated journey because a delay "would cause problems for the company's
client, Brass Exploration Ltd." the report added.
On June 30, 1998 the ill-fated aircraft was operating a flight on behalf of
Brass Exploration, lifting both personnel and material cargo from land to
base and hopping from rig to shore.
With Captain Montgomery Hartley in command, it landed at Don` Walker
Terminal at 1.00 p.m local time to pick several passengers to Port Harcourt.
It also stopped at Eket's Qua Ibom Terminal to pick a Bristow Helicopter
aircraft training chief, Captain Chris Cairns.
As it approached Onne, the pilot experienced some vertical vibration which
lasted about five seconds. The vibration stopped for about two seconds only
to resume with more intensity.
The vibration was so severe that Captain Cairns, who took over the radio
communication could not read any of the instruments because of the resulting
blur. The aircraft then pitched at about 20, dipped steeply to about 60 and
was flapping so violently that the left side door came ajar.
Subsequently, thick, deep blue smoke penetrated the cabin following which
the aircraft nosed down and on hitting the water, submerged.
Beside the five who died, two other passengers were seriously injured in the
crash.
The helicopter suffered substantial impact damage. Although the fuselage was
unshaken, the broken window enhanced rapid entrance of water which drowned
some of the passengers. Surprisingly, one of them, who did not fasten his
seat belt, survived.
Relevant components retrieved from the wreckage were taken to Air Accident
Investigation Branch (AAIB) Farnborough, United Kingdom where investigators
including officials of AAIB (UK); Accident Investigators Bureau in Nigeria,
representatives of Bristow Helicopters and Bell Helicopters conducted
laboratory tests on the components.
Findings revealed that one of the two drone links to the rotating swash pate
bolts was fractured below the head. Examination of the fractured surface of
the bolt revealed that it failed from corrosion fatigue.
Also, heavy corrosion was evident on the Bolt Shank and Trunnion bearing
inner member from where the fatigue emanated.
"During one of the 25/50/100 hours routine inspections of the helicopter,
one of the bolts on the swash plate trunnion bearing could not be removed to
enable the trunnion to be rotated 180 for greasing" it stated.
The report added: "The technicians/engineers however attempted to remove the
bolt with the aid of a hammer, punch and weight block, thereby subjecting
the bolt to an induced stress. The removal of the bolt was however deferred
until the time the swash plate was due for overhauling. The supervisor,
nonetheless, endorsed the untidy maintenance job as having been done
satisfactorily.
"The failure of the bolt was eventually responsible for the mal-alignment
and imbalance of the rotating main rotor control resulting into the vertical
vibration experienced by the crew before the crash" the report said.
One of the maintenance officials at Bristow, in a statement to the
investigators, confessed that they had trouble removing a drive link bolt
while carrying out a 25/50/100 hour inspection.
He said: "I went to the aircraft and tried myself to remove the bolt, using
a hammer and punch and weight block. After two or three attempts, I realised
that the bolt was not going to come free. There was no apparent damage to
the bolt threads, so I instructed an official"(name withheld) to lock the
bolt up and continue inspection"all the three of us were aware of the
situation regarding the bolt".
"For commercial reason, I elected not to replace the bolt and possibly the
trunnion bearing and drive link at the time, as the aircraft was required
for further (maintenance) programmes that day", the maintenance personnel
added.
To guard a recurrence, the AIB however recommended that:
- the ultimate fatigue life of the drive link to rotating swash plate bolt
of Bell aircraft be reduced. The mandatory air-worthiness limitations
presented for inspection of the control system bolt of 24 months should be
made 12 months;
- Bristow Helicopters should review the efficiency of its maintenance
personnel and re-organise the quality assurance unit.
- Immersion type of floatation system which responds to its float switch
making contact with water be prescribed for flights operating in the Delta
region.
- a Cockpit Voice Recorder (CVR) which is not susceptible to freak
vibrations should be in use.
It added that the fatality figure could have been lower if the aircraft
floatation system were those that were automatically activated when in
contact with water.
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