HOW did this happen? Boeing 737 loses control | Thomson Fly 3894

A Boeing 737 carrying 132 passengers spins out of

control

moments before landing, the pilots desperately try to push the nose down, but their plane is determined to climb as it does so, its speed drops and the pilot's agitators vibrate strongly indicating that are about to stop and fall from the sky, terrified passengers cling to their lives as the engines roar and the plane shutters will the pilots regain

control

of their plane or a simple misunderstanding will spell their doom. This is the story of Thompson's struggle.

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on the night of September 23, 2007, 132 passengers and five crew boarded a Thompson Fly Boeing 737 in Faroh, southern Portugal, most of the passengers returning from their late summer holidays in the Iberian Peninsula on a cold and boastful flight 389 from the United Kingdom. 4 would take them to Burnmouth on the south coast of England the flight time was 2 and a half hours while the passengers boarded the pilots were busy preparing the plane for departure the plane they were flying was a 12 year old Boeing 737 300 the 300 variant It was an earlier version of the 737s produced today, hence the hodgepodge of CRT screens and analog dials that can be seen here in the cockpit, but despite not having the amenities of a modern 737, it was still a safe and useful short plane. .

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was pushed back, the pilots began The two engines and began taxiing to the runway completing their checklists as they took command that night he was a 56 year old Captain, had been with the company for 18 years and had accumulated over 11,000 hours of flying experience in his time as pilot, however, most of this time was spent on the Boeing 75 7 and 767, he was still very new to the 737, having just been promoted to captain the year before, at this time he had just over 400 hours on the plane.

Sitting to the right of him was a 30-year-old first officer. He was also relatively new to the 737 and airplanes in general. He had just over 800 hours on the 737. Earlier he had found the turbo-boosted -8 engine that he built on. For most of his more than 3,000 flying hours that night, the first officer would be flying the plane while the captain acted as monitoring pilot. At approximately 9:30 local time, the first officer lined up the plane on the runway and turned on the lights. engines for take-off moments. Later, the plane was climbing into the sky, the pilots raised the flaps and turned north towards the United Kingdom.

It was a calm night in Faroh, but 1,000 miles north, in Bournemouth, the conditions were not so clement, it was a bit windy there, but the main problem was the cloud base, the pilots would not be able to see the runway until they were just 400 feet off the ground, about 30 seconds before landing, this was within safe limits, but in case the captain had decided to load additional fuel on Faroh, giving him the opportunity. opportunity to make two approaches to land in case the first one was not successful, everything was routine as the plane climbed to its cruising altitude and headed north over Spain as 11:00 p.m. approached.

As Flight 3894 flew through the clear night sky over the Channel Islands of Gery and Jersey, the captain having used the final minutes of the crews' relative camera to obtain the latest weather transmission for Burnmouth, the first officer would land the plane Tonight and as part of the preparation for descent, he would soon begin briefing the captain on the approach and landing. Behind the cabin door, a serene atmosphere had enveloped the cabin, some passengers chatting while others read silently bathed in the dim glow of the overhead lights. The hum of the two engines had lulled many others to sleep.

Three other members of the cabin crew were finishing duty at light and waiting for the sound of the seat belt signal coming on. This was the signal from the cockpit that the 737 would now begin. their descent At Burnmouth, the latest weather confirmed that the crew's earlier decision to take on additional fuel before departing Faroh was correct. Conditions at the airport that night were not ideal. The low cloud base meant that pilots would have to rely solely on their instruments. until the plane passed through the cloud at 400 feet, however, this was well above the minimum required for a well-equipped aircraft like the 737.

During his approach briefing, the first officer informed the captain that he was going to use the amount maximum flaps for landing 40° This was an unusual decision, there were only two destinations where full flap was needed. Bournemouth was neither of them. Full flap is only used when the runway is short, the 40° flap would increase the amount of drag by a significant amount along with the extra drag, however, would also increase the amount of lift the wings produce, which would has the benefit of allowing a slightly reduced final approach and landing speed. The combined effect of this is a shorter landing run due to low cloud base.

The first officer also advised that the approach would be an instrument approach using the runway ILS or instrument landing system. This gives pilots vertical and horizontal guidance to the runway, allowing them to land in very low visibility. The pilots then calculated the final approach speed based on the weight of the plane that night they would fight on final approach at 135 knots. This was fast enough to be safely above stall speed, but slow enough not to use too much runway. Landing everything ready. Flight 3894 now began its descent towards Burnmouth. It was a quiet night at the airport to save the pilot time and fuel.

Air traffic control cleared them to proceed to ILS for runway 26. The first officer descended and slowed the plane, turning it directly toward the extended center line of the runway. 26 in a few minutes he had positioned the airplane 11 nautical miles or about 20 km from the runway the airplane was level at 2500 feet and had decreased its speed to 180 knots the first stage of flaps had also been extended so far this approach was no It is different from the thousands of others that this experienced crew had flown to ease the pilot's workload, like most modern aircraft, the Boeing 73730 has an automatic throttle system, its function is to automatically provide the correct amount of thrust At any stage of flight, it also has several Modes that allow pilots to set takeoff power, climb power, and approach power with much more precision than pilots could by moving the throttles.

At this point the autothrottle was engaged in speed mode, which meant that whatever speed the pilots had set on the mode control panel so here the autothrottle would move the two engine levers to maintain that speed. These may seem like mere details but they are details that will play a crucial role in what is about to

happen

7 nautical miles from the runway about 13 km Flight 3894 intercepted the glide slope for runway 26. The glide slope is the vertical component of the instrument landing that guides the aircraft to the runway for descent. The autothrottle reduced engine power and the aircraft now began to follow the glide slope. towards the runway at a 3° angle the first officer asked for the landing gear to be lowered and flap 15 to be selected at this point the pilots were still in IMC or instrument meteorological conditions the fight would remain in the clouds until the final moments Before landing the 132 passengers were just minutes away from disembarking the plane, collecting their bags and returning home, but what

happen

ed next would put everyone on board in grave danger as the plane descended, the first officer selected. at a lower speed on autopilot, the thrust levers were moved all the way to idle to allow the plane to slow to this new speed, but just 20 seconds later something strange happened, the autothrottle silently disengaged, the light green autothrottle went off and a flashing red light illuminated to alert the pilots that the autothrottle had disengaged, but none of the pilots noticed that there is no sound when the autothrottle disengages, only this visual warning, the airplane It continued its descent while the pilots were blissfully unaware of the image they had in their heads. what the plane was doing was very different from what was actually happening because the plane had already been idling when the autothrottle disengaged, nothing in the plane's flight path changed when this happened, the plane just continued to descend and decelerate.

As usual, the autopilot, which is separate from the autothrottle, continued flying the plane, controlling the pitch and roll to keep it perfectly in the ILS. When the speed decreased beyond 150 knots, the first officer requested 25° of flap, but here is where the next critical chain arises in this An unfortunate series of events occurred when the planes decelerated, their wings generate less lift, being the force that keeps them in the air, to avoid this, the autopilot or the pilot who is pretending to move the horizontal stabilizer in the tailplane to be able to tilt the plane. Increasing this greater angle of attack which is the angle the wing makes with the oncoming air increases the amount of lift the wing generates so that it can still remain airborne even at lower speeds.

This movement of the horizontal stabilizer is called trim when the The autopilot flies the plane The autopilot trims the plane when the pilots fly the plane, they usually trim the plane using these little switches on the control columns here, so that as the As Flight 3894 slowed toward its final approach speed, the autopilot gradually brought the nose of the plane closer. up so that it still produced the lift it needed to keep it climbing at the target speed, apart from the rather important fact that the pilots had not noticed the autothrottle disengaging, everything appeared in order as the plane decelerated, the pilots continued spreading. the flaps, each flap setting has a recommended airspeed at which it should deploy, since the pilots were not used to landing with the full 40° of flaps, the first officer needed a quick reminder of the speed at which 40 flaps could be selected.

Speeds are printed on the front of the pilot control columns. The first officer turned on the light on his control column and read the indicated speed. Once the airplane went below this speed, he called for flaps 40 and the captain moved the stick to that position. When this was done, the first officer selected the final approach speed of 135.knots on the autopilot, what I didn't know of course is that this speed selection did nothing, the autothrottle was no longer controlling the air CRA speed, the throttle levers were still in the idle position right where were there when the autothrottle was disengaged, they would remain there until the pilots moved them or until the pilot turned the autothrottle back on in an airplane.

Speed ​​is how much planes stay in the air because they are moving through it fast enough. that the air feels thick on the wing so thick that it can support the weight of the entire plane without speed the air is just air and cannot support the weight of the plane slowly but surely the plane slowed down except that without throttle Water did not stop at 135 knots, instead it continued to slow down, the captain watched as the flaps extended to 40° once they were there. The landing checklist was now complete, the plane's speed had been reduced to 130 knots a few seconds later, after putting the checklist on top of the instrument panel, the captain saw that the airspeed had decreased At 125 knots, this was 10 knots less than it should have been and was getting dangerously close to stall speed.

The captain barked, the first officer responded by making a small movement forward. of the throttle levers, but it was too little too late, the captain took control, immediately slammed the thrust levers all the way forward, and made the standard call coming out of flap 15 to check thrust. It might be counterintuitive given how slow the plane had become, but the captain's instinctive decision to apply maximum thrust had actually been warned by Boeing. We will see why a moment before the engines could run, the pilot stick shakers shook violently indicating that the plane was about to take off. stall the air was now approaching the wing from such an angle that it could no longer flow gently over the upper surface the plane's speed was now dangerously slow at 110 knots and continued to decrease to its current altitude of only 1500 feet a stall could easily be fatal as the engine was slowly started up at full power the captain did what The only thing he could to avoid a stall, he pushed the control column forward to keep the nose down.

After a few moments, the engines had started at more than 80% of their maximum. power during a turn in an airplane like the 737, the increase in thrust from the low engines causes the airplane to pitch upward because the airplane rotates around its center of gravity, which is above the engines, increasing the thrust that comes out of the engines, the airplane naturally wants to turn upward. For this reason, Boeing's flight stroke training manual for the 737 warns against applying full power during a low-speed turn. Boeing knew that the pilots could do this instinctively if their speed had dropped too much and they knew that it would lead to a situation where controlling the pitch of the plane would become very difficult, the pilots were now about to experience firsthand why had issued this warning when the engines reached the maximum power selected by the captain, the autopilot disengaged and pitch was now released from the autopilot limitations began to increase.

The captain desperately tried to stop this pitching by pushing his control column all the way forward, but this was not enough. All he could move with his control column were these tabs here, the elevators at the rear of the horizontal stabilizer, the descent force they provided simply wasn't enough to counteract the enormous pitch generated by the thrust of the engines and the nose. high trim position that the autopilot had previously set as the airplane climbed its speed rapidly decayed the Shaker lever was activated again indicating that the airplane was dangerously close to stalling, this was now a life or death situation in the cabin, the terrified passengers couldn't even see what was happening through their windows, they were simply pushed back into their seats as the engines roared and the plane shook violently. but then for a moment the plane began to stabilize, it seemed as if the captain's action of pushing the control column all the way forward had slowed the plane's upward movement, the Shaker stick stopped and the plan airspeed began to increase now that they were flying fast enough to To be safe, the first officer moved the flaps to the 15° position, however, the pilots were far from out of danger, but the plane was still banked at more than 20 °, the captain was holding his control column all the way forward, something that is basically never done just to prevent the plane from pointing any further up, if anything changed he would have no control over the pitch of the plane, so a few more moments Later, when the R flaps followed Ed on the way up to 15°, the plane began to pitch at an even greater rate than before in the stress of the moment when one of the pilots began to involuntarily depress the left rudder pedal, now The airplane was not only pitching but was beginning to turn to the left as the flaps continued to retract, the pitch increasing further.

Also, the Shaker stick now rattled the pilot's controls for the third time, what else could the captain do? The engines were now providing more than enough thrust for the round, but the speed had become critically low due to the extremely high pitch of the aircraft, the captain was already applying nose-down elevator and yet the aircraft continued to pitch even further. high the first officer called pitch high the captain responded by saying that he was already pushing his control column all the way forward the first officer instinctively joined the captain at the controls holding his control column at its forward stop both men pushed with all their might in desperation to lower the nose and avoid a stall, but it made no difference, the elevators simply could not overcome the combined effects of the stabilizer trying to lift the nose and the engines rocking the plane.

Around its center of gravity, the plane was now barely 2000 feet above the ground, the plane continued its crazy trajectory banking up to more than 36°, something that would never happen under normal circumstances, the speed had dropped to only 107 knots and the involuntary action of the pilot's rudder. had brought the plane to an angle of 22° to the left, if this turn continued, the plane would soon roll over and plummet towards the ground quickly, the captain sharply pressed the right rudder and leveled the wings, but the terrifying roller coaster continuous. The plane continued pitching until reaching 44° while the pilots kept their controls fully forward and the shakers vibrated, then the inevitable happened, barely holding on at just 2500 feet, the 737 stalled, the nose dropped immediately, however this did not It was enough to restore a smooth air flow over the wings, in fact the angle of attack, that is, the angle that the approaching air makes with the wings, only increased.

The plane was now falling at such a speed that, as a result, the air was coming from below instead of from ahead. After this, its airspeed continued to decrease to just 82 knots, unthinkable for a 737, but the nose continued to descend for the next 10 seconds. When the pitch was reduced to 20°, the airspeed began to increase, the captain did something highly contradictory that he had learned in his training, he knew that a large part of the reason the plane had banked so much was that the engines were at high power to stop this I needed to reduce the thrust, it is not the easiest thing to do when they are already dangerously slow but it was the only way to regain control of the plane at this critical moment the captain put the throttle levers back to the 86% the effect this had was immediate the nose of the plane fell 15° in just 2 seconds finally the stall It was all over and with this new lower power configuration, the elevators had regained their effectiveness.

Cautiously, the captain let the plane's airspeed increase while he held the nose at 5° pitch up. The pilots, shaken, raised the flaps on the gear and climbed to 4,000 feet on the first The officer notified air traffic control of the maneuver and the captain had the plane return for another approach, as it turned out that the extra fuel that the As anticipated as the crew prepared for another approach, the first officer commented to the captain that during the first approach the autothrottle had not captured the speed. the one he had noticed, what he didn't know was that it was worse than that.

It wasn't that the autothrottle had simply failed to capture the selected speed, but that it had actually disengaged. Surprisingly, this wasn't exactly an uncommon event on this particular aircraft. The autothrottle was disconnected only on one in every 200 flights, this was a problem. not only in this particular aircraft but in this generation of 737 in general, that night the disconnection occurred in one of the most critical parts of the flight, the Final Approach, for this reason serious doubts arose in the subsequent investigation about why the Los Pilots had not noticed the autothrottle disconnection warning. It was the small visual cue sufficient to alert the crew during this high workload phase of flight.

The final report on this incident recommended that Boeing and the Federal Aviation Administration conduct a study on the effectiveness of the Boeing 737 300 400 and 500 Autothrottle Warning System and take necessary steps to improve crew alerts through this in On modern 737s like the 737 NG and 737 Max, it is much clearer to pilots when the autothrottle has been disengaged and, equally important, the autothrottles themselves are much more reliable. But ultimately, it is the pilot's responsibility to monitor the plane's flight path and detect any malfunctions that occur. In this case, the crew did not notice the speed drop below the 135 knots they had selected, leading to the captain carrying out an extreme maneuver that ultimately resulted in a stall near the ground, but in a curious turn. .

While the captain's application of maximum thrust was against Boeing's recommendation, it was not against the training he received from his airline's Thompson Fly quick reference manual. The crew operations manual did not advise against using full thrust or warn that pilots might need to use trim to control the pitch of the plane during a turn. This was a significant departure from Boeing's own guidance and ultimately led to a near-fatal accident in At 11 minutes past that night, Flight 3894 finally landed at Burant. Both passengers and pilots were shocked, but only the pilots were aware of how close they had really come to the incident.

This serious incident received little coverage in the press, but important changes occurred. In terms of flight crew training and reliability of warning systems, it is one of several similar incidents that have forced aviation as a whole to be as safe as it is today.