Witnesses were surprised when the 6,500lb chopper hadn’t exploded or burst into flames when it crashed through the roof of The Clutha pub.
Experts combed the wreckage of the twin-engined aircraft for clues as to why it had plunged “like a stone”.
One line of inquiry is that a fuel line was blocked or a faulty fuel gauge gave inaccurate readings, leading the crew to wrongly believe they had enough fuel for their journey.
Another theory is that the gearbox may have developed a fault and the rotor blades stopped turning – a “catastrophic mechanical failure”.
The crew of SP99, the stricken helicopter’s call sign, took off from their base, just two miles from the crash site, for a routine call on Friday night.
Flight Lieutenant David Traill, WPC Kirsten Nelis and their unnamed colleague strapped themselves into the Eurocopter 135, registration G-SPAO, before lift-off.
They had been sent out in search of yobs who had been trespassing on a railway line – a mission that would cost them their lives. Flt Lt Traill, 44, from Stirlingshire, was an experienced pilot who had served his country in the RAF. He joined up in 1987 and was posted to the first Gulf War in 1991.
He had more than 4,000 hours’ flying experience – 3,800 on Chinooks Friends of WPC Nelis yesterday changed their internet profiles to a black background with a thin blue line.
Eurocopter 135s have had safety concerns before. Operator Bond Aviation temporarily grounded 22 craft last year after cracks were found in the shaft of the main rotor during a routine inspection of a Scottish air ambulance.
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