Picking up where we left off a couple of weeks ago, the 737 MAX story continues to be the number one topic in the aviation community. Since the tragic loss of Ethiopian Airlines Flight 302 on March 10th, new information has come to light which could change the focus of the investigation and lead to further scrutiny of the air travel industry.
If you need a quick refresh, here’s the link to our original post which we published 5 days after the crash of ET 302.
Ok, grab yourselves a coffee and let’s dig into this new information.
Have investigators identified the avionics component potentially responsible for the uncommanded nose-down maneuver?
Investigators believe the 737’s Maneuvering Characteristics Augmentation System (MCAS) forced the airplane’s nose down in response to corrupted angle-of-attack (AOA) information.
Ok, but what is the MCAS and what was it designed to do?
As I mentioned two weeks ago, the MAX aircraft have new engines and a different wing profile than previous models.
- The engines, while more fuel efficient and powerful, are substantially larger than previous models.
- Additionally, the positioning of the engines, slightly forward of the wing, is different compared to the Next Gen models.
As a result of the changes, the aircraft now has a higher tendency to pitch up (nose up-tail down) than before. While not necessarily dangerous, the pilots need to be aware of their speed and angle-of-attack in order to prevent excess drag.
If the pitch becomes too high and the aircraft exceeds its safe angle-of-attack, the drag induced on the airframe can exceed the lift generated by the wings resulting in a stall. The correction, for the pilots, would be to push the nose down, increase the speed of the air over the wings, and regain the lost lift.
So, in short, the MCAS device is designed to push the nose down and prevent the aircraft from stalling.
So… if the MCAS was designed to prevent the aircraft from stalling and was only intended to be used as an emergency response, what triggered the response? Was it a genuine emergency?
Probably not… however, the data which was fed to the system may have been corrupted or erroneous (aka: incorrect).
After the Lion Air crash in October, it was revealed that the MCAS relied on a single sensor. Now, an experienced “AvGeek” might say…”Hang on, there are two pilots, two sets of instruments (for simplicity sake), and there’s a backup set of instruments, why would there be a single failure point for such a critical system”. I will get back to this point later on.
As far as we know right now, the MCAS on ET302 and JT610 responded to an erroneous stream of information. The information that was being fed to the system appeared to indicate an excessive AOA (see diagram above). As the system believed the aircraft was close to stalling (even though this was incorrect), the computers triggered the nose down response inputted by the MCAS.
For the pilots, they would have experienced an immediate reaction from the aircraft, in their mind without reason or warning.
Not looking very good for Boeing right now. Really, the system should take information from two sensors and let the pilots know if there is a disagreement. This is where the story starts to take a really interesting turn.
Why haven’t there been more accidents since the aircraft’s first flight?
The complexities of the disaster dictate that I should break this topic into sections, as such, I’ve examined the Pilots, the Aircraft, and the external circumstances in an attempt to answer this question.
Pilot Knowledge and Experience:
NOTE: This is a combination of personal speculation and known information as of June 6th. Subsequent sections have been edited as more information has become available.
Every airline will come out an say that their pilots have been fully trained and that they have the minimum number of hours required to fly the aircraft, but what does that really mean?
News recently, news came out that on the day before the Lion Air crash, the same aircraft had experienced the exact same problem. How did that flight land safely?
It was revealed that a “deadheading” pilot (a pilot in the cockpit but not officially on duty) was able to recognize the problem and guide the crew to shut off the auto trim feature (during a stall, the MCAS would command the Auto trim to push the aircraft’s nose down). This pilot had a working knowledge of the auto trim and knew how it could be disabled, thereby preventing the nosedive problem experienced by ET302 and JT610. Experienced may have saved the crew on that flight.
The important question, which has been the subject of many debates since the accident, is this: If that flight was recoverable, does it mean that the ET302 and JT610 flight crews were inexperienced and incapable of recovering their aircraft?
I’ll come back to this point later, but for now, the revelation that the aircraft could be recovered in the correct circumstances could be a confidence boost to Boeing.
Proper maintenance and understanding of the AOA Sensors:
Theoretically, if the 737 Max operators knew about the significance of the AOA sensors (as it pertains to the MCAS) they may have been more careful and observant in regards to aircraft maintenance schedules. It may sound simple, but if the sensor hadn’t given out faulty readings the MCAS wouldn’t have been erroneously called into action.
While many will rightly question the AOA’s single failure point (as we mentioned above), airlines could have relayed the importance of the sensor to their pilots had they fully known about the dangers that could result from the instrument’s failure. In reality, it seems that the Max operators were clearly not provided with this information and that definitely falls on Boeing’s shoulders; again, this is something I’ll return to.
It should also be noted that a freak failure of the angle of attack sensor cannot be ruled out and there has, as of yet, been no indication why the sensors in either accident fed the MCAS incorrect data. The industry’s overreliance on automation and the lack of a sensor disagreement warning or system switch remains a major talking point.
After glancing through the initial report and learning more about the circumstances, the answer to this question has changed considerably.
We’ve learned that the Ethiopian Pilots were facing a situation that severely limited their ability to manually trim the aircraft. This was something that was unknown when I began writing this piece. Whether the pilots knew the correct procedure (as per Boeing) or had sufficient flying skills to understand the nature of the problem and implement steps towards recovery, they still may not have been able to save the aircraft.
While the circumstances required for recovery aren’t fully known, we now know that merely diagnosing the problem and trying to apply the correct procedures aren’t enough to guarantee a safe landing.
Since we now know the two accidents occurred shortly after takeoff, it’s plausible to suggest that the surviving crew had enough time and altitude to recover the aircraft successfully. They were extremely skilled, but they also benefited from a bit of luck. However, luck can not be accepted as a reasonable measure of protection.
In order to truly prevent this from happening again, the aviation industry needs to understand why, and how, the aircraft was certified by the Federal Aviation Administration.
How was the 737 Max Certified by the FAA?
Due to the fact that the 737 MAX was “supposedly” constructed around an unchanged airframe, this process was expected to be completed relatively quickly.
In the case of the 787 Dreamliner, a clean-sheet design, the certification process required considerable flight testing and safety certifications; however, despite the important changes made to the MAX, Boeing and the FAA were able to certify the aircraft only 9 months after Airbus delivered their first A320-Neo.
It has since been suggested that Boeing and the FAA rushed the 737’s certification to maintain competition with Airbus. The A320 NEO and its sister aircraft (A319-NEO, A321-NEO) had been selling relatively well; Boeing was under pressure to respond and have the aircraft certified on time.
Why would the FAA certify an aircraft that had this serious a fault?
Short answer…they didn’t know.
Over the past few months, new information has surfaced about Boeing’s knowledge of the dangers associated with the MCAS. It has been suggested that Boeing played down the significance of the MCAS and signed off on the safety requirements without outlining all the details to the FAA.
In the aftermath of the two crashes, it has since been reported that the FAA let Boeing certify and sign off on certain portions of the 737’s flight test requirements. This presents a major problem for the industry. Typically, other aviation authorities, like EASA and Transport Canada, immediately sign off once the FAA certifies the aircraft for flight.
Hang on though, why would the FAA allow Boeing to complete portions of the testing?
Despite the obvious problem of having a potentially crucial system only taking data from one source, Boeing deemed it insignificant and not a serious threat. Without sufficient financial resources and under pressure to certify the aircraft to maintain American business, the FAA allowed the aircraft to be certified.
To me, this story has a political element which cannot be downplayed.
Over the past few years, the United States Government has cut funding to a number of crucial government agencies: the FAA, the EPA, and the FDA, just to name a few. Corporations have been given the freedom to operate in a slightly deregulated environment. It was unfortunately not a surprise to me to learn that the aircraft’s certification was expedited through the FAA.
How can this be rectified to prevent future disasters?
The United States government has created a conundrum: the voting public believes that their government agencies are doing their jobs ethically and properly. In reality, the agencies that are there to protect the population actually serve the interests of the largest bidders: the corporations.
It has become clear that the rest of the world can no longer accept the FAA’s certification without question. I truly believe that Transport Canada and EASA will run their own testing and delay certification of the aircraft until they are satisfied in its safety.
This could lead to significant changes in the aviation industry. It’ll be interesting to watch Boeing try and regain momentum and convince the current operators that the problems with the aircraft can be rectified.
That being said, laden with a potentially unrecoverable failure, the 737 Max could be out of action for a considerable length of time.
It is not out of the question to see this series of failures as the death of the 737 MAX. While I’m hopeful that the aircraft lives to see another day, it cannot be allowed to fly without the proper procedures being put in place. Boeing needs to be reminded that its number one priority has to be the safety of the flying public. Until then, the aircraft has to remain grounded.
From our perspective, any new developments will be mentioned on our twitter account. Once/if the aircraft is re-certified for flying, I may consider concluding the saga in a “Hot Air” segment.
Until then, thanks for your continued support!