Sam Elliott-Gibbs | mirror.co.uk
Three British Airways jets were grounded at Heathrow due to an insect infestation discovered just seconds before take-off by horrified pilots.
The aircraft were hauled off the runway between June 9 and 11 when the plane’s speed sensors were found to be malfunctioning.
The Department of Transport’s Air Accidents Investigation Branch launched a probe into what they called ‘serious’ incidents.
Two of the jets were roaring down the runway when the pilots successfully abandoned take off after the creatures had crawled in and caused chaos.
A third plane is believed to have been moving towards the runway when the pilots noted a similar error, and returned to the stand.
Investigations later revealed that insects had crept into the aircrafts’ air speed sensors, known as pitot tubes, causing blockages which gave false speed readings.
Similar incidents are known to have caused aircraft to crash in the past, because it confused by recording inaccurate airspeed data.
All three of the BA jets are believed to have been on the ground for periods of between three and seven days when the insect contamination happened.
Normally aircraft in storage are required to have special covers over their pitot tubes to help prevent insects or dust getting inside.
The coronavirus pandemic is said to have put more aircraft at risk of the issue due to flights being cut and more airliners stored for longer periods on the ground.
The incidents at Heathrow happened between June 9 and 11 this year when temperatures at the airport had soared to 26C, creating ideal conditions for swarming insects.
The most serious involved a BA Boeing 777-200 which was taking off to fly to Accra, Ghana, on June 11.
The jet was rolling down the runway at nearly 100mph when the pilots realised there were ‘unreliable air speed indications’ from all three of their pitot tube systems.
It is believed that the crew used their brakes and reverse thrust to safely bring the jet to a halt.
Passengers were delayed for more than five hours before a second jet was brought in to fly them to Accra.
The earlier incidents are said to have involved Airbus A320 jets on short haul flights.
One had a rejected take off due to an ‘airspeed discrepancy’ noted in two of its three pitot tubes while the other was found to have an error caused by a single blocked tube.
The Civil Aviation Authority put out a safety bulletin to aircraft operators warning of the dangers of infestations immediately after the cases came to light.
The bulletin stated: “Initial feedback suggests a form of insect infestation may have contributed to these events.”
It warned operators to be alert to the risks of returning aircraft to service after ‘extended parking’ during the pandemic.
The bulletin added: “Crews should be made aware of this potential issue, reminded of the importance of the speed checks during the take-off roll and the actions to be taken in the case of a discrepancy, as well as the appropriate unreliable speed indications for their aircraft type should they discover the issue once airborne.”
A separate AAIB investigation was carried out after a Wizz Air plane abandoned its take off when its speed sensor suddenly failed as it roared down the runway at Doncaster Sheffield airport at 140mph.
The incident happened in June last year when the Airbus A321 was being transferred to Stansted airport with no passengers on board after being parked up for 12 weeks during the first coronavirus lockdown.
It was later discovered that one of its pitot tubes contained three tiny insect larvae.
The report found that the insects could have entered the tube even when sensor covers were fitted because they did not provide a complete seal due to possible problems with creating air pressure changes.
The crash of a Boeing 757 with the loss of 189 people in 1996 was blamed on the pilot having become confused by a faulty air speed indicator soon after taking off from the Dominican Republic for Frankfurt.
Investigators ruled that the most likely cause was that a mud dauber wasp had nested in one of the pitot tubes while the plane, operated on behalf of Birgenair, was on the ground for the previous 20 days.
A British Airways spokesperson said: “Safety is always our highest priority and we, like other operators, are conducting additional checks in line with the CAA’s recommendations.
“As the AAIB investigation continues it would not be appropriate to comment further.”
Aviation consultant Paul Beaver told the Mail on Sunday : “The most important thing is that the BA air crews were absolutely on the ball in picking up this problem. It indicates how well they are trained and they need to be congratulated for being alert.
“There are always pre-take off checks and then the pilots carry out further checks when they are moving down a runway which is what happened here so there was no danger.
“But insects in pitot tubes are a fundamental problem for anything from a glider to a big airliner, and these incidents show that something was awry with procedures. It shows the importance of having continuous vigilance.”