mduell

MCAS still has nothing to do with stall, despite frequent media confusion.

They need to execute to capitalize on it. The A380 EIS woes and market miss, A350 launch six-peat, A400M delays and cost overruns, and A320neo EIS woes are really hampering their ability to take advantage of any Boeing issues.

BF263533

Your thoughts on this analysis:

“MCAS is a longitudinal stability enhancement. It is not for stall prevention (although indirectly it helps) or to make the MAX handle like the NG (although it does); it was introduced to counteract the non-linear lift generated by the LEAP-1B engine nacelles at high AoA and
give a steady increase in stick force as the stall is approached as required by regulation.”


“The LEAP engine nacelles are larger and had to be mounted slightly higher and further forward from the previous NG CFM56-7 engines to give the necessary ground clearance. This new location and larger size of nacelle cause the vortex flow off the nacelle body to produce lift at high AoA. As the nacelle is ahead of the C of G, this lift causes a slight pitch-up effect (ie a reducing stick force) which could lead the pilot to inadvertently pull the yoke further aft than intended bringing the aircraft closer towards the stall. This abnormal nose-up pitching is not allowable under 14CFR §25.203(a) "Stall characteristics". Several aerodynamic solutions were introduced such as revising the leading edge stall strip and modifying the leading edge vortilons but they were insufficient to pass regulation. MCAS was therefore introduced to give an automatic nose down stabilizer input during elevated AoA when flaps are up.”

14CFR §25.203 Stall characteristics.

(a) It must be possible to produce and to correct roll and yaw by unreversed use of the aileron and rudder controls, up to the time the airplane is stalled. No abnormal nose-up pitching may occur. The longitudinal control force must be positive up to and throughout the stall. In addition, it must be possible to promptly prevent stalling and to recover from a stall by normal use of the controls.

737 MAX - MCAS

spin88

MCAS was added because moving the new engines forward and up, along with modifications to the tail changed the response of the MAX during climb, and in particular as you climbed the engine would provide forward lift, which would cause a nose up.

Boeing could have simply trained people that the plane flew differently, and trained them to address the situations where lift would accelerate during a climb, but they were trying to game the system to sell the MAX as "just like a NG, so no new training needed".

The problem is that someone at Boeing - contrary to what was submitted to the FAA, made the MCAS have the ability to make multiple very major (2.5 degree) inputs.

IMHO there is absolutely no reason for those kind of inputs unless you are concerned about stall. My understanding (to be corrected if I am wrong) is that the FAA was told that MCAS would add .5 degree of input, not 2.5 degrees.

It appears (or is reported) that this much higher degree of MCAS input was put in to prevent stall conditions during climbs when the auto pilot was off. See e.g. https://theaircurrent.com/aviation-s...em-mcas-jt610/

Perhaps this is wrong, but it appears to have been Boeing that turned it into a sub-rosa stall prevention system.

LarryJ

MCAS is not a stall prevention system. It is exactly what the name says; a Maneuvering Characteristics Augmentation System.

As AoA increases, pitch control forces should also increase. That is required by certification regulations. Due to the lift from the larger engine nacelles, as you pointed out, the pitch forces do not increase sufficiently.

I don't know if the reduced pitch forces are enough to meet certification requirements as a separate type rating. It doesn't really matter as the airplane is not, and will not, be operated by a single type. Either way, the result is the same--the pitch force had to be increased in those situations. MCAS increases the pitch force, i.e. makes the nose heavier, by introducing a nose-down bias through the application of nose-down stabilizer trim. This provides the increasing control forces that are required by certification regulations. It also replicates the pitch feel of the NG models on which most MAX pilots will be dual-qualified.

737s, including the MAX, have conventional stall characteristics. Stall warning is provided with a conventional dual stick-shaker system with each side's stick-shaker deriving input from the respective side AoA indicator. This type of system is common in jets and turboprop airplanes of all sizes. When an airplane does not have conventional stall characteristics it needs additional help to avoid stalling and/or to recover when a stall occurs. I have flown several aircraft with such systems including the J32 (Jetstream), CRJ, and DC9.

Both the J32 and CRJ had stick-pushers which violently and abruptly push the control column forward with such a force that it is impossible for the pilot to override.

The DC9, with its T-Tail, could get into a 'deep stall' in which the wings block airflow over the stabilizer and elevators in such a way that the elevator would not respond to control-column input (it is an unpowered surface operated by a control-tab) making it impossible to recover from the stall. This was addressed by adding a hydraulic actuator that would push the elevators toward the nose-down position when the elevator positions failed to respond to a nose-down control column input. Later DC9s, starting with the DC9-50 series, had long strakes added to the sides at the nose to further control the airflow over the tail during high-AoA operations.

Those are a few examples of what stall prevention, or stall recovery, systems look like. No 737 model needs, nor has, any such systems. It meets all stall-related certification requirements without them.

BF263533

GHISLAINE DE CLAREMONT lawsuit filed in the United States District Court Northern District Of Illinois, Case: 1:19-cv-03297 Document #: 1 Filed: 05/16/19, alleged:

" 1. This action seeks justice for GHISLAINE DE CLAREMONT, who was killed in the March 10, 2019 crash of Ethiopian Airlines Flight 302 (ET302) only minutes after take-off from Bole International Airport in Addis Ababa, Ethiopia. " .........

"50. Pursuant to the FAA's Airworthiness Standards for Commercial Aircraft1: "No abnormal nose-up pitching may occur.... In addition, it must be possible to promptly prevent stalling and to recover from a stall by normal use of the controls."

1 14 CFR Sec. 25.203(a) — Stall Characteristics."

"51. Despite knowing that the Boeing 737-8 MAX had aerodynamic handling defects, BOEING pressed on with the development of the airplane and created MCAS to mitigate the risk of a potential stall and to force the 737-8 MAX to handle more like the Boeing 737NG. However, MCAS failed to mitigate such a risk and on or before March 10, 2019, BOEING knew and/or should have known of that failure but did not take action thereby putting the flying public at risk, including the decedent. Such acts and omissions demonstrate reckless disregard and conscious indifference for the safety of the flying public at risk including the Decedent."

Link to the court complaint:

https://www.kreindler.com/Recent-Dev...ing-Filing.pdf

These are only "allegations" at this point in time subject to proof on summary judgment or at trial.

PotomacApproach

I know there was a lot of chatter pre-crashes about the 100 MAX 10s coming into the fleet, and expanding domestic lie flat service as a result. Are these plans still on? And if they are, is this really the right plane?

mduell

There's been no official news or leaks yet. Looks like a great plane for UA market fit.

Discussed in Should United Cancel Its Order for 100 – 737 MAX 10s, & Order the A321neo?

AirbusFan2B

travelinmanS

jsloan

Neither has the MAX 10, since none have been delivered.

The MAX 10 will be the most scrutinized derivative launch in years. There's no actual reason to expect any problems with it.

I hate to break it to you, but if UA wanted the A321, they'd already have an order for it -- they'd have converted the A359 order into an A321 order. UA is more likely to wait for the 797 than they are to buy the A321. The only scenario I could see where UA would take the A321 is if there's a major problem with Airbus's order book (e.g., a couple of large customers declare bankruptcy) and Airbus makes UA a sweetheart offer.

I do. I love the MAX 9, and I'm excited to fly the MAX 10. I've only flown the A321 once, and I was thoroughly unimpressed. Of course, it was an AA flight, and I was somewhere in the hinterlands of the plane; I imagine it's better closer to the front. Still, nothing about the experience made me wish that UA would take them into their fleet.

travelinmanS

jsloan

I felt no terror and rarely use the lav on a narrowbody. And the "narrower seats" thing -- I get it, I really do. But what people always overlook is how rarely the extra inch of space usually matters. When I'm feeling squeezed in a Y seat, it's rarely by half an inch. I generally fly window seats in order to move as far away from the middle seat as I can, and I do that on the A320 series as well as the 737. To hear some people tell it, Y is comfortable on the A320. It's not.

What I do like about the MAX (at least on UA) is the airy feel to the cabin with the "Sky" interior and the space bins.

cv11nyc

BF263533

Never made the Constellation or Electra but I did the DC-3, Convair 580, FH-227, BAC 111, Convair 880, DC-8, 707 Grumman Goose, DC-9-10, Martin like 404 or 440, Concorde, etc.

I really enjoyed United's 737 in the early 1970's, but it started getting a little tired in the 1980s with that 737-300 and those oval engines sitting low to the ground. The 737 is one of the first planes I flew almost 50 years ago, and now it may be one of the last planes I fly in my lifetime. Boeing with the 737 MAX was apparently inspired by the movie Groundhog Day. When the 737 first came out there was a TV show called Greenacres. One character was Mr. Haney. (Google Mr. Haney Greenacres and watch a video). He would always say, "do I have a deal for you." Dress CEO Muilenberg up as Mr, Haney and do a Greenacres MAX remake. The 737 program should have faded into the past with Greenacres.

halls120