A 50-year-old design came back to haunt Boeing with its troubled 737 Max jet

The airframe isn't getting old. In fact there's nothing left of the old airframe but the general shape of the windshields.

It's the type rating approval process that got old and caused all this.

Lifting body designs might work for cargo but modeling exercises have shown they aren't practical for passenger service. The rows of seats would be wider, and so the passengers out at the ends would be subject to too much vertical movement during turns. This would cause motion sickness for many passengers, or at least be unpleasant. And more emergency exits would be needed for the same passenger count in order to meet evacuation time limits.

It's hard to think of many other legacy systems that have been around since at least the 60s like the 737 MAX has. The NYC subway system is one that immediately comes to mind.

Went back to the well for marketing reasons. Keeping the shape, but only the shape, so they could use the 737 name.

I’m no airplane expert but I find the trend lines of the industry interesting and one trend has been how fuel prices and long lead times on fuel efficiency has lead to formerly continental planes now flying intercontinental. AirBus has really done this well and airlines love to be able to reuse resources. With the MAX there is a sense that airline execs are spooked by a new plane since it requires a ton of new training and maintenance outfitting. So Boeing, possibly smartly, tried to create what these airlines would pay for (a fuel efficient airplane) that would marketable be super similar to a very popular plane. But this lead to rushing the process and making too many affordances and hiding the differences from airlines and training material for fear of spooking business execs worried about cost.

Right, but it sound like the aerodynamics have been deteriorating model-by-model, as they move away from the original design.

This creeping change must be really hard to regulate right. A terrible new design you could refuse to certify, but a terrible one which is only a few percent worse than the one your predecessor certified a decade ago... it would take a lot of confidence to say no.

"Under certain circumstances" is, as I understand it, close to stall. Many planes have less-than-desired stall characteristics. The tendency of T-tail planes to go into an unrecoverable deep stall comes to mind.

Or have you ever flown a Cessna 152 or 172? They have the same tendency to pitch up strongly when power is advanced at low speeds. This is probably the most common training aircraft in the world, and yet have a behavior that may cause them to stall at exactly the most inopportune time. And they're flown by students, not airline transport pilots!

The 737 MAX does not require the MCAS. The pilots could be trained to expect and handle this characteristic. (And they are, as it is apparently, to a lesser degree, present on all 737 models.)

The big problem lies in the design of the MCAS system and the fact that it was decided to rely on this and not train pilots on the new behavior.

We're told that MCAS only activates with the autopilot already off.

I agree with you that pilot training doesn't seem to be a plausible answer given that the Lion Air crash was world news, resulting in retraining, and yet that wasn't enough.

Pilots can fly planes with unusual characteristics when properly trained. That is the point of the type rating. I feel the 737 MAX needs its own type certificate distinct from the rest of the 737s and that should solve the problem, since the MAX has very different flight characteristics in certain situations.

Either that or ground the plane permanently for being poorly designed and unsafe with any amount of training.

If the FAA does anything else, it will harm my faith in the organization, which is already at a recent low.

NB: Jet pilot, not 737 pilot.

Pilot training is a major reason air travel is so safe.

> One hopes that the pilot a) knows and b) remembers to turn off the autopilot when the emergency starts.

This is where training kicks in. After hitting the scenario 10 times in the simulator, the pilot doesn't remember; they _do_.

The solution isn't so much "more pilot trainimg".

It's that pilot training wasn't done that absolutely needed to have been.

A three page if even that description of the system, and it's inputs/outputs/controls should have been sufficient for a pilot to be able to build up a mental model to deal with a faulty AoA sensor, and modify their piloting technique to stay within a more conservative maneuvering envelope while operating the plane.

Whether that would have been sufficient to prevent both disasters I don't know, but it sure seems like it would be a small trade off that even in the absence of any other system hardening could have made the difference between no survivors, and an emergency landing.

Consider that before WW2, pilots had direct connection between the control and moving the surface. After WW2, planes got too big and heavy for that, and hydraulic boost was added. Starting with the 747, where it is not credible a pilot could control it with muscle, the switch was made to fully powered surfaces.

The trouble with that is the pilot's controls simply crack open a valve, and hydraulics do the rest, meaning the pilot gets no feedback via forces on the control column. He'll "overcontrol" the aircraft leading to a crash. The solution is the addition of a "feel computer" which pushes back on the stick making the airplane feel like direct control. Safe flying relies on the feel computer working properly.

Also, the travel of the control surfaces is automatically reduced as speed goes up, because full travel at high speeds will literally tear the airplane apart.

So right there are two flight critical computer systems on jets, and modern air travel would not be possible without them. Each produces an illusion to the pilot.

Trim would never be a separate airfoil because that would be horrendous for efficiency. Instead they have an all-moving tailplane.

They could have prevented this issue by slightly increasing the tailplane size to restore stability margin, but they didn't presumably for development cost and fuel efficiency reasons.

Trim controlling stabilizer, yoke controlling elevator, and elevator being unable to counteract the more extreme ends of trim settings, is part of the original 737 design. They all behave that way, and 737 pilots are aware of this, and know they must neutralize trim to have ample elevator control.

However, only the 737 MAX has MCAS, and MCAS doesn't take airspeed into account. An appropriate corrective action for a low airspeed stall, will be way too aggressive for a high airspeed stall (a rare event, suggests overly aggressive dive recovery leading to a stall). And designers + regulators assumed that pilots would treat such behavior the same as an ordinary runaway trim incident, but does it seem ordinary or is it a shockingly bad overcorrection?

We've seen many times the scenario where pilots become so surprised at a particular situation that their rational ability to work through the problem can be compromised. Yes, transport pilots are substantially trained to avoid such a compromise, but problems at low altitude combined with the lack of a consistently positive rate of climb is an urgent situation. Pilots are hyper aware that recovery from either a dive or stall consumes a huge amount of altitude, which you simply don't have at low altitude. That itself could delay proper decision making: i.e. automation has betrayed us for unknown reasons, disable it now.

With MCAS disabled, what's the 737 MAX stall behavior like? Is it meaningfully easier to unwittingly get into a stall?

I think I read that longer landing gear wouldn't fit into the fuselage without major reconfiguration.

Not a direct answer, but what you’re more or less asking is “why did they not modernize the 757 instead?” The answer is type ratings. Pilots can fly certain classes of planes based on common training. I.E. the 757 and 767 are common enough you can be trained for both at the same time. The issue with changing geometry of the 737 is you have to then retrain pilots against a new type instead of letting them take an orientation course on the new plane.

Honestly if the accidents did not happen we’d be calling them geniuses. After all, that’s why the 737 is the best selling plane ever.

Designing longer landing gear might invalidate the common type rating, as the plane's entire fuselage and wings would be higher off the ground during take-off and landing, which might be non-trivial. Plus it would have different heights compared to previous 737s, which could cause problems with jetways, staircars, maintenance vehicles, luggage ramps, etc.

There's not many things they could've changed about the existing design without it being enough unlike the existing design to effectively count as a new aircraft (logistically if not certification-wise). They could move the engines, but they couldn't change the ground clearance.

Yeah. It is strange that they were the last regulatory org to do so. . In America basically every governmental body is in the pocket of big business.

N.B. no American carriers have crashed a MAX, and they are flying quite a few of them.