Boeing’s Updated MCAS Software
Yesterday, Boeing announced that it had completed its update of the MCAS software which was now with the FAA for certification. This seems like a good time to bump the conversation back to the front page, as there’s been some very interesting issues and articles posted into the comments of the previous articles.
First of all, let’s look at the software update. Boeing have aimed to provide additional layers of protection when the AoA sensors are giving bad data, which appears to have been the case in the two fatal 737-Max crashes.
The additional layers of protection include:
Flight control system will now compare inputs from both AOA sensors. If the sensors disagree by 5.5 degrees or more with the flaps retracted, MCAS will not activate. An indicator on the flight deck display will alert the pilots. If MCAS is activated in non-normal conditions, it will only provide one input for each elevated AOA event. There are no known or envisioned failure conditions where MCAS will provide multiple inputs. MCAS can never command more stabilizer input than can be counteracted by the flight crew pulling back on the column. The pilots will continue to always have the ability to override MCAS and manually control the airplane.
These updates reduce the crew’s workload in non-normal flight situations and prevent erroneous data from causing MCAS activation.
In addition to the news, the BBC have published a long piece about the fatal 737-Max crashes. It’s aimed at a mainstream audience without the experience that most of us have, but it’s worth reading, I think: What went wrong inside Boeing’s cockpit?
Going back to the comment thread, I’d like to call out some of the specific links that have been posted.
Danni posted Six Minutes to Disaster: How Ethiopian Air’s Pilots Battled the Boeing 737 Max and asked if anyone could shed light on the effect of the airspeed on the acciddents.
Andy commented on how it just keeps getting worse for Boeing along with this link: Boeing altered key switches in 737 MAX cockpit, limiting ability to shut off MCAS
Mendel got caught in the spam trap (sorry again) with a piece by Marcel van den Berg about the design change, specifically numbers 28 and 29 on his list: Overview of many failures by Boeing in designing the Boeing 737 MAX. He also posted this article by Jon Ostrower which sheds some light on why they couldn’t use the manual trim: Vestigial design issue clouds 737 Max crash investigations.
I’m sure this will be in the news for quite some time to come, especially with predictions that the Boeing 737 Max might be back in the air by the end of the month. Feel free to keep the conversation going here; I’m very much enjoying the articles and insights and I’m sure other readers are too.