23 years ago today, on the eve of January 8, 1989, British Midland Airways Flight 92 departed London Heathrow bound for Belfast International airport. 40 minutes after departure, the flight would end in disaster, forever changing the lives of the 118 passengers and eight crew on board.
British Midland Flight 92, a three-month-old Boeing 737-400, registration G-OMBE, landed at Heathrow at 18:45hrs having completed the first of a return sector to Belfast. The 737 departed at 19:52hrs with the First Officer handling the departure.
After take-off the aircraft followed departure instructions and began climbing up to flight level (FL) 350. As the aircraft passed through FL283, part of one fan blade in the No 1 (left) engine detached, causing a number of compressor stalls. These triggered airframe vibrations and smoke to pour onto the flight deck as well as flames from the engine, which were visible from the cabin.
Unfortunately, the crew believed these were from the No 2 (right side) engine that had been damaged and had begun the process of shutting it down. On throttling the No 2 engine back, the vibrations reduced, leading the crew to further believe they had dealt with the problem engine. The No 2 engine was then shut down and the crew initiated a diversion into East Midlands Airport. The No1 engine continued to provide thrust and stabilized slightly due to the thrust lever being set at idle throughout the descent.
As the crew were on the approach for Runway 27 there were high levels of vibration from the No 1 engine, after increasing the No 1 engine throttle for more thrust, the crew triggered a secondary fan failure and the engine lost power. Now with two inoperative engines, the Captain instructed the First Officer to restart the No 2 engine. However, at this point the plane was below the speed at which a successful restart could have been achieved.
At 2.4nm from the runway threshold and only 900ft above the ground without sufficient thrust, the aircraft began to sink below the glide slope. In a desperate attempt to stretch the glide to the runway the Captain raised the nose of the aircraft, but to no avail. Moments later, the ground proximity warning system activated and as the Captain addressed the cabin with the words “PREPARE FOR CRASH LANDING”, the stall warning ‘stick shaker’ triggered.
At 20:24:23 the aircraft struck the ground off the eastern side of the M1 motorway before bouncing and crashing into the western embankment breaking into three main sections, a mere 900m from the landing runway. 39 passengers were killed at the scene with a further eight later dying of injuries sustained in the crash. Miraculously, there was no traffic on the motorway at the time of impact.
What went wrong?
Through the investigation of Flight 92 and two separate, near-identical incidents that took place in June 1989, it came to light that the engines were suffering from severe vibratory stress leading to metal fatigue. Unfortunately, at the time, the certification testing was only required to be carried out in a laboratory environment where it was later discovered that the airflow was unrepresentative of what occurs in-flight at high altitude. The vibrations, which the engines were displaying during the certification test, were in fact milder than what was being experienced in real flight conditions.
Following the investigation and subsequent incidents, changes were made to ensure that all turbine engines would be tested at all altitude conditions and power settings, replicating the experience these engines would encounter during everyday service.
Flight Crew shutting down the wrong engine
Through a series of factors, the pilots erroneously shut down the fully functioning No 2 engine. The investigation concluded that the stress of the environmental factors, such as noise, smoke, and vibrations, were outside the training and experience of the pilots. This may have led the crew to make a rushed decision without thoroughly checking the engine instruments, which clearly showed the No 1 engine was the root cause.
Then, in an unfortunate coincidence, as the No 2 engine was throttled back, the vibrations reduced, which led the pilots to falsely believe their actions were correct. Regrettably, despite much of the cabin, including three cabin crew, witnessing the flames from the No 1 engine, this information never made it to the flight deck.
Following the disaster, greater emphasis was placed on Crew Resource Management (CRM) training for pilots and cabin crew. CRM is designed to encourage the effective use of all available resources to enhance safety through efficiency, reducing errors and avoiding excess stress.
Incorporated with CRM, pilots are trained to use models such as T-DODAR, an acronym that gives a clear structure to decision making, helping to counter any hinderance in thinking ability caused by the startle factor of an unexpected event. The final step in T-DODAR is the review, which is a constant reminder that what was originally decided may no longer be the best and safest course of action.
The NITS briefing is now also used to share and relay important information to cabin crew, giving them the chance to clarify any uncertainty.
When used effectively, these two models can help to encourage the sharing of different mental models, perspectives, and information to ultimately formulate a plan of action.
Loss of life
On impact, due to the floor collapsing in several places, many seats detached from their fixings. This led to passengers experiencing a secondary impact, mainly severe crushing against the seat in front. Although the cabin structure and seats met the standards of the time, it was concluded that fixings should be made to withstand greater forces.
Many passengers, despite taking the crash position, flailed during impact, resulting in fatal head injuries for most of the victims. Scientists soon began developing a more robust brace position, which still stands today.
Aviation disasters, although a tragedy, are seldom in vain. They almost always drive change and encourage even higher standards. While any error is foremost an error, it also presents an opportunity to learn, develop and ultimately improve flight safety.