Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1] 20

[itsmoked]

Indonesian 737 Max 8 - Splashed

Most reports I've seen mention the aircraft had an 'undisclosed issue' before take-off. Does anyone know what that was?

Surely the crew was in contact and reporting something during the relatively long disaster.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ornerynorsk]

Seems that there had been some technical issues reported for the prior flight, people reporting unusual engine noise, etc. Can't find the link to the article right now.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[zeusfaber]

Couple of days ago, the BBC was reporting a discrepancy between captain's and first officer's altitude and ASI displays.

A

 

[hokie66]

One recorder has been recovered, they didn't say which one.

Another thing not reported yet that I have seen is whether the same crew was on the doomed flight as on the one before. There were some issues on that flight, and were said to have been fixed. If the pilots carried over to this flight, they can't help, but if they were relieved, they could probably shed some light.

 

[thebard3]

Here's a link to a forum where lots of aviation experts are discussing this crash. I follow the forum regularly and you'll get breaking there first.

https://www.airliners.net/forum/viewtopic.php?f=3&t=1407217

Brad Waybright

It's all okay as long as it's okay.

 

[hokie66]

Reports are that the pilot of this aircraft's previous flight issued a "Pan Pan" alert, requesting to return to the airport, then cancelled it when the plane started flying satisfactorily. It was also reported that passengers on that previous flight saw a pilot walking down the aisle with a big manual. Before this crash, Lion Air had a seven star safety rating, now reduced to six stars.

 

[itsmoked]

A prior flight passenger said the plane dropped suddenly "panicking the passengers". Seems like the next load of passengers got the complete ride.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[hokie66]

I think it is highly unusual, maybe in violation of aviation rules in most countries, for a Pan Pan alert to be overridden with the flight continued as if nothing had happened.

 

[TehMightyEngineer]

I think it is highly unusual, maybe in violation of aviation rules in most countries, for a Pan Pan alert to be overridden with the flight continued as if nothing had happened.

Possibly against the airlines internal operational specifications but not against any aviation rules I'm aware of.

Pilots actually frequently cancel emergencies. For example; sudden icing beyond the capabilities of the airplane to fly through. Declare emergency and use pilot authority to descend without getting clearance from ATC. Get below the icing and then you can cancel your emergency and continue on like nothing happened. You will of course have to explain later why you called an emergency and could get in trouble if they find you either caused an emergency through reckless action or canceled an emergency when the emergency still existed.

Pan-pan is even more likely to be canceled; it essentially indicates you have a priority situation that requires special attention. Something like a broken radio or a standby instrument failure or a jammed landing gear. It's not an emergency yet but you may need something special (direct route to destination, going into a holding pattern, emergency equipment standing by, etc.), if you're able to fix the problem in the air you can let ATC know that you fixed it and proceed on.

Clearly they made a mistake to continue on. It's just a matter of whether that mistake was reasonable and/or not their fault.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[hokie66]

There have been a number of instances of instrument failure due to clogged pitot tubes. Insects? But surely properly trained pilots would be able to overcome that type problem.

 

[Alistair_Heaton]

hi all just registered to answer some questions

I used to be Finite Element Mech Eng in a previous life. Now I fly aircraft for a living.

I am not rated on the 737 only Dash 8 Q400 and previous Jetstream 31/32/41. The Q400 is a modern digital efis system aircraft and the Jetstreams old analogue tech.

First of all the emergency declaring. There is nothing stopping you trying to cancel if you sort out a problem. But its a two way thing once ATC knows you have an issue they can adjust the emergency level as they see fit and the pilot has no control over it. I won't go into the ins and outs of various situations but I have in the past declared and then cancelled and continued to destination and even operated the next flight immediately. 2 mins filling a report out and not heard a thing about it again. Also somethings such as Hydraulics failures are major issues on certain aircraft types and on others such as the Jetstream its more of an annoyance. This is to do with how the controls are powered or not in the case of the Jetstream. BUt if ATC hears anything to do with hydralic failure they will presume the worst thinking you going to go off the end of the runway due to needing to do a flapless high speed approach and have no brakes or steering on the ground. Jetstream we would pump the gear and flaps down, land and taxi using the prop reverse and front wheel castoring. Not a huge issue.

Instrument failures are a bit of a bitch. Analogue instrument aircraft in some ways are easier to trouble shoot and work out what's wrong and deal with.

Digital aircraft with efis the instrumentation comes from the airdata computers which take the environmental data and anther box does magnetic heading and navigation and displays it on the screens. There are at least two and they cross reference each other and when they disagree they tell the pilots. There is also a back up system which has its own pitot and static system and is run on a backup electrical supply with sperate battery support for if the main electrics go down.

What the pilots sees if something goes wrong is xxxxxx mismatch on the primary flight screen it won't trouble shoot. You then have to go into a quick reference handbook to reconfigure the displays to remove the faulty data input after comparing the 3 information sources and hopefully going with the two that agree. Its a two person check and double check. One person is meant to fly the machine the other one trouble shoots.

Now the departure is high work load and everything has to work towards getting away from the ground. The further away from the ground you are the more time and space you have to sort things out. Something happens below minimum safe altitude and you have a problem.

Now not all pilots think the same way, as an engineer flying a plane is just an energy equation which you can change the variables using the controls. So what to do is very logical to me with the flight profile. Your just playing with 4 variables thrust drag lift and weight.
The if you stick the nose at an up angle to the horizon with a set amount of thrust and the wings level it will climb within a range of speeds depending on weight. You don't actually need to know your airspeed to know you are safe. This to me is glaringly obvious and how I have treated instrument failures in the past from single engine piston right the way through to the 30 ton q400 (although I haven't had a problem with the Q's instruments yet with a mismatch). It works every time. To be honest its my normal method of flying pitch power equals performance. The speeds vary with weight but what your actually doing is setting a most efficient angle of attack which never changes.

Now other pilots brains don't seem to work the same way or as fast working out what's wrong. They "chase" the needles so they apply control inputs to make the numbers right. Once the numbers are right they then realise that the other data is not as expected then after a period of recognition then transfer to other methods of defining the flight profile. Now this goes back to the very first lessons flying how they fly. Personally when I was a flying instructor I didn't give my students any instruments and they had to learn to look out the window for attitude and set the power by ear. Then when they had that sorted they got the instruments. But because the habit was set initially they were not fixated on airspeed or other instruments depending what they were doing. Just attitude and power. Flying in cloud with the attitude indicator failed is another issue but we can do it.

This dealing with instrumentation failures is a hot topic in the sim sessions and has been since the Air France AF 477 accident.

Please note in no way am I inferring anything to do with this incident, At least once a year depending on the training syllabus sometimes more there will be an item in the sim to do with instrument failures. The low level just as the gear comes up are shall we say interesting. Personally I learn more about dealing with the human side of things during them with the reaction of the other pilot than I do from the actual handling of it. You can have two people with completely different ideas what's actually happening and what to do to fix it. And what you don't want is two people fighting over control inputs that's always fatal.

Most incidents are a combination of human and equipment, we will have to wait until the CVR and FDR are analysed to see what actually happened and no doubt the year after next there will be something in the sim training syllabus so we can all learn from it.

 

[Spartan5]

Thanks for sharing that with us, Alistair_Heaton. Very good perspective on the challenges and responses of properly trained pilots.

 

[Alistair_Heaton]

Avionics trouble shooting is always a problem as a lot of the time they test out SATIS on the ground and only show issues when the aircraft is in flight. vibration thermal expansion pressure changes are all factors.

Thankfully these days most machines have huge number of variables data recorders which get downloaded every 30 hours of flying anyway. They record stupid numbers of variables from the primary flight instruments through to the amount of times the toilet pump is used.

This data is used to monitor the pilots performance ie they run it all through a computer after its downloaded and checks to see if we have been sticking to SOP's or handling the aircraft in a none approved manner.
The other side is all the tech data for the engines and other systems. At least these days a tech problem the technicians can see the raw data instead of having to use pilot reports of problems. We also have a bookmark ability in the cockpit so if the engines fart or something weird happens we can press it and it dumps a marker in the datalog so it flags where in the 30 hours of data the issue occurred.

There are all sorts of cultural issues going on as well and shall we say philosophy's. I am lucky that I work for a company that the CEO was a pilot in his younger days and has dictated a clean techlog policy.

tech faults with aircraft get stuck into 5 classes.

AOG plane grounded until its fixed

A requires fixed in a small number of flights or time period.

B 3 days

C 10 days

D 120 days.

Its all control by a thing called minimum equipment list the more safety related the issue the shorter the period there is to fix it. If the problem is not mentioned in the MEL then your grounded.

Clean techlog means that the problems are fixed ASAP and things are not aloud to build up or left until the end of the limit. It means the engineering stores have to carry a huge number of spares which some company's would only order on demand knowing that they could get them inside the MEL limits. It costs money. But... I have only had to ground an aircraft down route twice in 2 years/1000 flights working for them. We are at the top of the league tables for on time departures and its a rare event with have to cancel a flight due aircraft tech. For me its obvious that his policy works. If its more cost effective than ordering on demand I really don't have a clue.

Training we spend 25% more time in the sim that legal min and also have 20% more ground school every year.

Some pilots are really not so lucky. Every entry in the techlog is an argument and training is considered a box ticking exercise. I really don't have a clue what this company's operating philosophy is like.

 

[btrueblood]

Any chance you could share what airline that is?

 

[davidbeach]

It may not be one selling tickets. Several years ago I’d heard from a pilot on one of the major carriers that the FedEx pilots got far more simulator time than any of the people haulers.

 

[thebard3]

New posts on airliners.net forum cite a recent press conference stating that the previous 3 flights experienced unreliable airspeed data.

Brad Waybright

It's all okay as long as it's okay.

 

[TehMightyEngineer]

But surely properly trained pilots would be able to overcome that type problem.

Short answer, yes. I'm not trained in large aircraft but am an instrument rated pilot so can share generalities. Pilots are definitely trained to fly without accurate airspeed or altimeter indications. I've actually had an in-flight altimeter failure due to water getting into the static air port during a foggy day. Quick fix as the plane was equipped with an alternate static air system, so it was a non-emergency. Generally these can be trained for safely and resolved without issue. You may have even been on a flight that had a failed instrument in-flight and not even known.

That said, instrument failures can be some of the most dangerous problems in aviation because they're sudden, possibly intermittent, and difficult to diagnose in a chaotic situation. There are redundancies of course, but the redundancies are not always complete replacements for the failed instrument. I'm not qualified to talk about the full procedure in a large, modern airline, but generally the procedure is to identify the instrument giving false readings, disable or ignore it (hard to do!), and utilize reliable alternative sources of info of which there should always be at least one. The plane will keep flying just fine but it becomes much harder to ensure the plane can be flown safely by reference to instruments alone. Due to this danger the systems are very robust and capable, but it still isn't perfect. A lot of flight training is spent focusing on preparing for sudden instrument failure.

Air France 447 was the extreme example of sudden instrument failure essentially startling the crew into an improper response, combined with some shortcomings in the design of the Airbus:

https://en.wikipedia.org/wiki/Air_France_Flight_447

Not sure if that happened here as well.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[debodine]

Alistair_Heaton and TehMightyEngineer have both touched on an important point when it comes to the pilot/machine interface for diagnosing problems in the stress of an emergency. Some instrumentation, at least with regard to the signals/data, are closed loop systems. For example, GPS. The GPS satellites contain data streams that works with the on-board receivers and the mix of various GPS satellites being used, typically 4-5 satellites for the heavy iron on which I have most of my experience. The GPS receivers on-board and the satellites in the constellation being used can talk back and forth to detect, isolate, ignore and/or call up redundant satellites without pilot intervention. Thus the data presented to the pilot is reliable unless a flag and/or warning notifies the pilot not to use the data.

Air data systems are (at least as far as the data provided to the pilot) not closed loop systems. What I mean is there is no satellite constellation, ground station, airborne station or any other system in place outside and independent of the aircraft against which the air data system can compare what it THINKS is correct, and thus no feedback outside the aircraft itself to say to the air data system, "Whoa, the data you are feeding to the pilot sucks, throw a flag!"

Thus the air data systems can really only compare against each other. On some aircraft there are actually four air data systems: Pilot, CoPilot, Standby and Alternate. This gives a lot of redundancy unless the situation that is affecting one system affects all systems in a similar manner.

To illustrate: In a GPS constellation the probability (I don't have hard data in front of me, using relative terms) is very unlikely that more than one satellite will develop the same malfunction at the same time as they are thousands of miles apart and fully independent from each other. However, even on an aircraft with four air data systems, if all the pitot tubes and/or all of the static ports are affected in a similar manner by the same phenomenon (say for example rapid onset of icing at altitude), the various systems still agree with each other even though all of the systems are now lying to the pilots.

Of course physical separation on the exterior of the aircraft and other means (software processing) are used to try and provide as much independence as possible along with opportunities to find deviations that can provide warnings to the crew, but it is not as easy to provide independent comparisons between on-board systems as it is with signals and data originating outside the aircraft to use for cross check.

 

[TehMightyEngineer]

Debodine is 100% correct. In my in-flight incident with my altimeter, water in the static port causes the altimeter to get stuck at an altitude. Because it's rare to be stuck perfectly stable, I saw my altimeter fluctuate from a steady change during a climb to suddenly stopping and then jumping a few hundred feet. Clearly a failed instrument and obviously unreliable. Verified my standby altimeter was showing the same (they share the static port), and selected alternate static air supply. Problem went away.

However, if it stuck perfectly at one altitude and I wasn't paying attention, I might have kept climbing or even started descending without knowing it. I might see an airspeed that was then too high or too low for what I expected and start messing with the engine or pitch to try to "fix" it. This confusion could cost precious time while the airplane is slowly getting out of control. I would like to think I'm smart enough to avoid this but better pilots than myself have messed this one up.

Until they develop a closed loop system for the primary instruments (attitude, heading, airspeed, altimeter) the only thing I can do it keep training as much and as often as possible. Thankfully GPS has made things way easier and newer tech like synthetic vision is greatly simplifying instrument flying.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[IRstuff]

GPS is still an afterthought in aircraft, I think.

GPS provides both groundspeed and an independent altitude. Ever since Air France, it struck me as odd that we're not able to built a better air speed sensor and/or figure out some way to use the GPS altitude and speed data to cross-check the air data.

TTFN (ta ta for now)
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