23 November, 2018

Error in programming flight management computer nearly caused disaster in Belfast.

Missing centre light BFS runway
Photo AAIB
On the 21st of July 2017 a Sunwing Airlines Boeing 737-86J, registration C-FWGH took off from Belfast International Airport at 1539 but only just made it into the air after it struck a supplementary runway approach light, which was 36 cm tall and 29 m beyond the end of the runway.  

In a report issued today by the UK's Civil Aviation Authority's Air Accident Investigation Branch detailed how the aircraft took off without sufficient power to meet regulated performance requirements following a number of errors including the incorrect programming the 'Flight Management Computer - FMC'.  An outside air temperature (OAT) of -52°C had been entered into the FMC, the actual temperature outside the aircraft was 16°C. This meant the aircraft was attempting to take off with just 60% of its available thrust and was slow to travel down the Belfast runway. This low acceleration of the aircraft wasn't recognised by the crew initially, not until the aircraft was rapidly approaching the end of the runway. The report says the aircraft rotated at the extreme end of the runway and started to climb away at such a low rate that it would have spelt disaster at many other airports. The flight deck crew did not apply full thrust until the aircraft was approximately 4 km from the end of the runway, at around 800feet. 

There was no damage done to the aircraft which continued on to its next destination of the Greek island of Corfu, with passengers none the wiser to the dangerous start of their journey to the sun. The  AAIB states in its report that the benign nature of the runway clearway and terrain elevation beyond, with the lack of obstacles in the climb-out path which allowed the aircraft to climb away without further collision after it struck the runway light. The report also states that had an engine failed at a critical moment during the takeoff, the consequences could have been catastrophic.    

The pilots didn't notice the incorrect temperature had been inputted to the FMC, they didn't notice how slow the aircraft was going down the 07 runway until quite late in the takeoff roll. The crew took no action to either reject the takeoff or increase engine thrust when they did realise they were going slow compared to normal operations. They didn't apply full thrust power until the aircraft was struggling to climb after it had just managed to get off the ground. 

The aircraft’s FMC did not have the capability to alert the flight crew to the fact that they had entered the incorrect OAT into the FMC, although this capability existed in a later FMC software standard available at the time, however, Sunwing hadn't updated the FMC software for some time. 

.Error in programming flight management computer nearly caused disaster in Belfast.