Boeing to release software upgrade for the 737 MAX 8
March 26, 2019
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The 737 family of jets have been hugely successful since their introduction back in 1967 but the tragic loss of two of the latest MAX 8 variants in recent months has cast a long shadow and the apparent similarity of the sequence of events leading up to the two incidents has led Boeing to issue a worldwide temporary flight ban on the model. The crash of the Lion Air aircraft last October and the current Ethiopian Airline aircraft incident seem to have similarities, as the Minister of Transport of Ethiopia announced recently after initial examination of black box information.
The air-accident investigations are still ongoing and we will not know the truth until their final reports are published but some industry insiders have speculated that recent changes to the 737 design could hold the key. The MAX 8 version of the 737 uses modern fuel-efficient CFM Leap engines which are physically bigger than the original power plants. They need to be mounted higher up and further forward on the airframe, which originally created a handling problem when the aircraft was flying at high angles of attack, particularly at low speeds when landing and taking off.
The surprising thing is that all safety critical applications will generally employ three identical systems and perform a majority vote on the outputs so that a bad signal from any single system will be ignored. Preliminary information from the event in October last year suggests that it would require faulty information from just one Angle of Attack (AOA) sensor for the MACS system to issue continuous nose-down ‘corrections’. The crew can easily disable the system by switching both STAB-TRIM cutout switches to their CUTOUT positions. It emerged in the last few days that investigators of the October crash were able to determine from cockpit recordings that the crew found themselves in a situation their training had not prepared them for and they were unable to disengage and avert disaster.
The CEO of Boeing has confirmed that the company is hard at work on a software upgrade for this particular aircraft type which they plan to have completed within ten days and they will also be revising the associated pilot training program.
The air-accident investigations are still ongoing and we will not know the truth until their final reports are published but some industry insiders have speculated that recent changes to the 737 design could hold the key. The MAX 8 version of the 737 uses modern fuel-efficient CFM Leap engines which are physically bigger than the original power plants. They need to be mounted higher up and further forward on the airframe, which originally created a handling problem when the aircraft was flying at high angles of attack, particularly at low speeds when landing and taking off.
MCAS
Boeing solved the altered handling characteristics by introducing the MCAS (Maneuvering Characteristics Augmentation System), which uses sensors to measure the aircraft’s angle of attack and issues down-stabilizer control inputs when the system senses that a stall condition is imminent.The surprising thing is that all safety critical applications will generally employ three identical systems and perform a majority vote on the outputs so that a bad signal from any single system will be ignored. Preliminary information from the event in October last year suggests that it would require faulty information from just one Angle of Attack (AOA) sensor for the MACS system to issue continuous nose-down ‘corrections’. The crew can easily disable the system by switching both STAB-TRIM cutout switches to their CUTOUT positions. It emerged in the last few days that investigators of the October crash were able to determine from cockpit recordings that the crew found themselves in a situation their training had not prepared them for and they were unable to disengage and avert disaster.
The CEO of Boeing has confirmed that the company is hard at work on a software upgrade for this particular aircraft type which they plan to have completed within ten days and they will also be revising the associated pilot training program.
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Discussion (10 comments)
Charles Hirst 6 years ago
Sauli Palo 6 years ago
Boeing was stating just three days ago that the plane is safe, which was shown on BBC World News. I find this utterly unbelievable and shameful to over 300 passengers killed in the two crashes.
Same news also showed Max 8 Pilot Manual (2500 pages), where MCAS system is mentioned only once: in a list of abbreviations. How can you expect pilots to act correctly when MCAS takes control?
Lauren A Scott 6 years ago
SR-71 6 years ago
As noted by another user above, it was not Boeing to do that, the opposite is true.
Boeing reputation is going to be severely harmed by its behavior.
Andrew Couldrake 6 years ago
Also how can an airplane manufacturer sell a safety monitor as an additional extra ?
precesseur 6 years ago
Bill Marsh 6 years ago
Richard Cooke 6 years ago
Like a bump on the runway, might be 1.51g, that would trigger the over 1.5g so the interrupt would be triggered. But no one programmed this interrupt, so the interrupt would not be cleared, so we only get rubbish from the accelerometer, or gyros.
BRENDON WHATELEY 5 years ago
Aviation safety has always improved based on incidents from which new things get learned and improvements made to prevent them from recurring. The lack of MCAS documentation could be simply because it was an extension of the existing auto-trim and anti-stall systems. Resolving the sensor input problem could be achieved by following the existing runaway trim memory item checklist. They probably considered that sufficient, but based on the relatively inexperienced crews in the two crashes, improvements needed to be made.
Boeing was working on an improvement after the first incident, which was delayed by the government shutdown. I've seen very little comment on that delay which was outside of Boeing's control. Also, the FAA has not been properly funded for years. And in a climate of cutting regulation and costs, they were pushed into relying on Boeing far more than might be prudent. So blame congress for not properly funding the organization to do its job properly.
Finally, the optional safety features probably would not have made much difference to the outcomes, because the situation was giving the pilots too much information already. An additional; warning light would not have necessarily prompted the right actions in the face of the other conflicting readings, stick-shaker, and alarms. Better crew training could have made a big difference.
AlanLloyd 5 years ago
Also in my earlier life developing & fitting auto-pilots & autolanding systems we injected failures into the system to check that aircrew could recover if one occurred. Was such failure simulation done with the MACAS..