Boeing 737 Max: the "Blowback" problem provides a new explanation of the dive

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The "Blowback" problem provides a new explanation for the maximum immersion 737

| Reading time: 4 minutes

Gerhard Hegmann

Like here, on the runway of Hongqiao International Airport in Shanghai, 737 Max 8 aircraft are currently on the ground Like here, on the runway of Hongqiao International Airport in Shanghai, 737 Max 8 aircraft are currently on the ground

Like here, on the runway of Hongqiao International Airport in Shanghai, 737 Max 8 aircraft are currently on the ground

Source: picture alliance / dpa

Continuing to look for the actual cause of the accident, experts are discussing a new theory. As a result, the "flashback" effect should have ensured that the pilots could no longer prevent the fatal dive.

NThe cause of the crash of the two new Boeing 737-Max 8 aircraft in Indonesia and Ethiopia has not been fully documented. But the US aircraft manufacturer is progressing with the approval of a new version of the MCAS flight software, which probably plays a key role. In the future, it will no longer intervene vigorously and repeatedly in flight control, reports the "Wall Street Journal". However, it is not yet clear when the current ban on flying Max models will be lifted.

The Air Traffic Control Authority of Canadians and Europeans wants to verify this time what is being presented by Boeing and the US FAA. "The EASA is doing everything possible to restart and resume the plane as soon as possible, but only if it has full confidence that it is safe", declared the European Aviation Authority , WELT. If Boeing and the FAA presented to the Europeans all the details of the MCAS software at Max-Zulassung 2017, the authorities declined to comment. Since 2011, there has been a mutual recognition of Airbus and Boeing airline registrations.

Nearly 350 people lost their lives in the Boeing-Max crashes in Indonesia and Ethiopia. After that, an extensive discussion began on the cause of the accident. The range goes from the design defect in the Spartriebwerke models, to the MCAS flight software, which is connected only to a trim sensor, to the warning displays in the passenger compartment only for a fee, to the pilots' training gaps or to the # 39. ; deception of the US Air Safety Authority (FAA) in the approval. The FBI also investigates.

New "flashback problem" theory

Now comes another thesis on the intensive course in the spotlight. After that, the pilots probably could no longer avoid the dive. Experts talk about the "problem of returning to the past". In simple terms, it is understood that the air pressure at high speed at low altitude is so strong that there is a rebound of the desired deflections of the control surfaces, such as the elevator. So the pilot can no longer drive the plane up or down. The dynamic pressure is stronger than the hydraulic modifications to the control surfaces of the aircraft.

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The cockpit of a Boeing 737 Max 8

Pilot for Boeing 737 Max 8

The reference to the blast effect comes from the respected fighter jet pilot and the industry expert Bjorn Fehrm of the Leeham News Industry Service and is also discussed extensively in professional aviation forums such as www .pprune.org. There is an agreement, but also skeptical comments.

In principle, the warning applies against premature explanations in the event of aircraft accidents. However, a fatal error chain crystallizes. After initially supplied a position sensor broke incorrect data. Consequently, the MCAS flight control software has constantly started the "upside down" flight maneuver, in which the aircraft trim is modified by the electrically adjustable spindle tail plane. The Lion Air pilot corrected this maneuver more than 20 times.

Now comes the new hypothesis: according to the previously known speed data of the Ethiopian Airlines flight, the speed at low altitude became very large during the descent, exceeding the so-called maneuver speed (Va). Therefore the deflections of the complete rudder without overloading the structure of the aircraft are no longer possible. Thanks to the anti-return effect, the pilots were no longer able to use the hydraulically powered elevator with all the strength to avoid diving.

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The question remains unanswered when the accident in Ethiopia, because the pilots, a very experienced captain with over 8000 flight hours and a copilot with only 350 flight hours on 737 models, the MCAS system at the beginning of flight did not shut down. Boeing and the air traffic control authorities had specifically indicated after the incident in Indonesia, while the controversial software was being issued.

Although Boeing is now running a new version of the MCAS flight software, it is still unclear whether further modifications to the Max models are needed. In addition, passenger confidence must be regained. For example, the Indonesian airline Garunda wants to cancel a major order placed in 2014 for 49 737 Max models at a list price of just under $ 5 billion. This was justified by the concerns of passengers facing the Max model. In industrial environments, however, reference is made to the fact that cancellations are not so easy. However, with the subject of passenger fears or delays in deliveries, airlines may request additional discounts and damages.

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