I think the problem was likely that there was no way to fix this particular mounting configuration for the larger, more efficient LEAP engines without a significant redesign of the whole airframe. Or just give up on the higher efficiency, which would be a non-starter from a competitive standpoint. Its competitor the A320neo already has significantly larger engines (in terms of overall diameter and fan diameter) but it also has correspondingly higher ground clearance.
I’ve never seen anyone claim that the 737 MAX has dangerously poor handling, only that too many pilots were not aware of the uncommanded nose down stabilizer trim issues. There are many serious questions to be answered about how this situation was allowed to happen, but with appropriate pilot training and additions to the flight manual, and the software changes currently in the works, it ought to be fine. I’m sure that what a lot of airlines are worried about is continued passenger aversion to this particular airplane even after all the fixes. And of course the big question currently hanging over everything is what the flight data recorder will reveal in this latest accident.
Article linked below has some new information with the following comment:
“Flight 302 was just three minutes into its flight, the person said, and appeared to have accelerated to even higher speeds, well beyond its safety limits.”
I’m not sure where this “speeds well beyond its safety limits” information is coming from. The article refers to “publicly available data”, which would be this, which is also the source of the information about erratic vertical speed. Just for reference, the maximum speed shown before communication is lost at around three minutes was 383 knots at around 8500 ft MSL (but barely 1500 ft AGL, and only briefly). For comparison, I checked the track log for a typical normal 737 MAX 8 departure and after three minutes it was doing about 300 knots at about 7000 ft MSL (about 6500 ft AGL in that specific case).
The maximum speed for a B737 MAX is 340 knots (and Mach 0.82 but that is irrelevant at low altitude). On the face of it, 383 knots is indeed significantly faster than max operating. However that’s not the end of the story. The speed data from Flight Radar 24, which is where your link leads, is ground speed (GS). The speed limits for aircraft are referenced to indicated air speed (IAS). The actual speed of the aircraft through the air is the true airspeed (TAS). The indicated speed will always be lower than the true speed with the error increasing with altitude. The ground speed is the true air speed plus/minus the wind.
So was it exceeding the speed limit or not? That depends on what the wind was. If it was flying at the speed limit at 8500, the true airspeed would have been around 395 knots, so a nil wind ground speed of 383 knots would actually be within the normal operating range. If there was a 50 knot headwind though, that would equate to a true air speed of 434 knots and an indicated speed of 370 knots, well in excess of the limit.
Confused? The moral of the story is that it is unwise to read too much into data from the likes of FR24 without having a very good understanding of what that data actually represents.
What I can say is that a normal indicated speed for a passenger jet at 1500 feet AGL is somewhere between 130 - 200 knots. It depends greatly on the departure profile flown, some airlines accelerate from relatively low altitudes, some from much higher. Noise abatement procedures figure heavily as well.
Richard, thanks for the clarification. I was aware of the basics you describe but had completely forgotten that the speed data from all of these tracking sites are ground speed – a fact I should have remembered well since I track flights a lot due to family travels and I have occasionally noticed flights apparently going supersonic for certain periods, simply indicative of a strong tailwind up in the jet stream!
But are you sure you meant AGL in the above comment, and not MSL? Why would Indicated Air Speed be affected by distance from the ground rather than pressure altitude (essentially, MSL)? From that perspective one notes that the Ethiopian flight was doing about 383 kts (ground speed) at about 8600 ft MSL. My reference flight at the same point of approximately three minutes elapsed (08:29:40 timestamp) was doing 304 kts (again, ground speed, to be clear) at a slightly lesser altitude (2400 m, or about 7800 ft MSL). This seems to me to be comparable speeds at similar altitudes above MSL, but as you say, the winds could have been much different. Still, I’m not sure on what basis, given the above, one could positively conclude that the flight was exceeding safe airspeed.
I know next to nothing about airplanes or commercial flying, but I suspect that things ”go wrong” far more frequently than I would really want to know about.
However, I also know that there are multiple systems and back-ups and fail safes so that in the vastest majority of cases, the passengers end up safely on the ground, often not even knowing that something went awry. I include humans in as safety systems - the pilot, the ground crew, the air traffic controllers.
My amateur impression of aircraft safety is that a plane usually crashes for only two reasons: 1. A really catastrophic event, 2. Multiple system failures.
I’m guessing the Boeing Max flights went down because of case #2 - and something inherent to the aircraft is causing it. If something, anything is hindering the “safety system” known as the pilot from fixing a problem, that is very bad.
ETA : I didn’t mean to imply the pilot is just a redundant system. I mean that he or she can serve as the backup to another system gone wrong. Autopilot acting weird? Pilot flies the plane manually. Engine throws a part and breaks a window mid-flight? Pilot figures out how the get everyone on the ground with minimal loss of life.
My own stereotype of Germans is that they are practical - sometimes to the point of being a bit amusing about it.*
I’m sure the Germans would have loved to do it, but if they felt like they couldn’t do it to the highest standards for whatever reason, then it doesn’t surprise me that they would say no.
Case in point - Angela Merkel’s remarkably efficient wardrobe. No criticism from me on that front - As a woman, I find her system quite admirable, and I’m really sort of jealous of it.
My view is that accidents happen for one or more of three reasons;
Stuff breaks
People make mistakes
Only God controls the weather
All accidents trace back to one or more of those three.
The only problem is that while that’s a theory to be explored it is not PROVEN. It’s important to know what the actual problem(s) is(are) rather than making assumptions. Make the wrong assumption and miss the real root cause you could wind up with more accidents down the line and none of us want that.
It’s possible (though, again, not proven) that the Lion crash could have been a software problem and the Ethiopian crash due to debris being sucked into the engine(s), leading to loss of control and a crash. In which case they’re not the same cause and maybe the Max line of 737’s is OK.
I did mean AGL. During take off and subsequent climb the aircraft will become airborne at whatever the calculated indicated air speed was, let’s say 140 knots (it depends on many factors including weight and flap setting), it will then climb at a slightly higher speed, eg 150 knots, to the acceleration altitude. The acceleration altitude is the altitude at which it’s calculated it is safe to accelerate to a faster speed, normally 250 knots, and retract the flaps. Although it is expressed as an altitude AMSL, it is actually defined by height above the ground. Additionally, an airline will have a minimum acceleration altitude. The acceleration altitude may be higher than the minimum in order to out climb a building or hill, but it can’t be lower. Where I work our min acceleration altitude is 1500’ above the ground. 250 knots is then flown until any air traffic control speed restrictions cease to apply.
The initial climb profile then is all based on height above ground and you can’t compare speeds of aircraft if one of them is relatively low AGL because it won’t have accelerated to its final climb speed yet.
Whether or not 383 knots is above the Vmo for the B737, it is certainly going very fast, a good 200 knots faster than would be typical for the initial climb.
As I understand it the new engines change the balance enough to warrant a more aggressive stall prevention profile. It’s designed to push the nose down and will stop that momentarily if the pilot uses the trim switch. It then resumes the nose-down maneuver until the pilot uses trim again. Under the right conditions It keeps doing this. The changes to the programming includes additional sensors and a limit of one cycle of the nose down-trim.
I imagine it gets a bit confusing if a pilot has to fuss with this for any length of time. It would be like fighting a ghost because of the time delay between manual trim input and counter computer trim input.
Really? You can’t imagine why an African country with a significant Muslim majority might want to shop around and make sure the black boxes go to an impartial country, even if that takes some time?
Rather than hand them over to an American airplane manufacturer and an American government agency, and then trust that the American government agency will be impartial between the large American company and the African operators of the airline?
Seems perfectly reasonable to me that they want to make sure the investigation is carried out by a relatively neutral agency, even if it takes a bit longer to arrange.
I don’t think it’s a center of gravity issue, it would be relatively easy to lengthen the fuselage aft of the wings to fix that. I think it’s more of a thrust angle problem, I suspect they couldn’t (or wouldn’t for efficiency sake) set a thrust line that would cancel out the pitching moment of the engines when power is increased. Normally that would require the engines to point down so that the thrust vector would be as close as possible to the aerodynamic center of the airplane but doing so may A) further lower the front of the engine nacelle reducing ground clearance, B) direct the engine exhaust right into the underside of the wing and C) reduce fuel efficiency because part of the engine thrust would be spent in pushing against lift.
AFAIK most airliners with wing mounted engines pitch up when power is increased, but in this version it seems the effect is so pronounced it can overwhelm the flight controls.
I still believe the plane is intrinsically flawed because of this, like people have said here accidents are usually the result of a chain of events going wrong and this issue of the engine placement is a permanent issue with the plane that is kept in check by systems that can and have failed killing many people.
“It can’t be fixed” is not acceptable, if the engine configuration leads to an airplane that makes it susceptible to losing control then they need to change that even if it means recalling all the airframes and rebuilding them. Back at the beginning of passenger jets the de Havilland Comet turned out to have a serious design flaw, the square shape of the windows caused too much concentrated stresses on the fuselage that led to two airplanes blowing up like balloons killing everyone on board. The reaction was to redesign the airplane not throwing up the arms and saying that it would be too much work to do so.
Boeing already spent the “we’ll fix the software” card after the crash in Indonesia, if this new crash was caused, at its root, by the design compromises they made with the engine placement then they need to fix that root cause.
Oh, I understand the political realities and the reasoning behind it… but I can still disapprove of the delay in the investigation. I am just baffled at the time delay in finding a third party. There are plenty of NTSB-equivalents around the world capable of doing the work.
It is not the thrust line. The new position of the engines causes the nacelle to create lift at high angles of attack resulting in a pitch up moment. If it was related to increasing thrust it would happen at any angle of attack. A pitch up with increasing thrust is normal behaviour for most aircraft and does not need to be designed out of an airframe.
The deal is that if you pull back on the column it should become progressively harder the more you pull. This is normal safe behaviour. What the Max was doing was decreasing the force required as the angle of attack got higher, this leads to a tendency for the aircraft to pitch further and stall. The Max could not be certified with this characteristic and Boeing opted to solve the problem by effectively disguising it with the MCAS system which artificially increases the force required by trimming in the opposite direction (nose down).
It sounds like the German equivalent was concerned that because it’s a new black box with new software, they weren’t comfortable taking it on. That suggests that there wouldn’t be very many safety boards with the technical capabilities to do the job.
