News Ethiopian 737 crashed on way to Kenya, 157 people on-board

[Evil_Onyx]

I have recently been reading about the Concorde and the Crash. It was not a single point of failure, It was a combination of a Maintenance errors on the Concorde landing gear, over filled fuel tanks (Against the manual), The flight crew was under time pressure (did not wait to burn off taxi fuel), The Flight Engineer shut down a good engine without telling the pilots and the aircraft was overweight. It was just the FOD that day on the runway that made all the other factors matter.

 

[Urwumpe]

I have recently been reading about the Concorde and the Crash. It was not a single point of failure, It was a combination of a Maintenance errors on the Concorde landing gear, over filled fuel tanks (Against the manual), The flight crew was under time pressure (did not wait to burn off taxi fuel), The Flight Engineer shut down a good engine without telling the pilots and the aircraft was overweight. It was just the FOD that day on the runway that made all the other factors matter.

Thats an alternative theory that does not even fit the available evidence. But it does like to pop up, because it is close enough to the real information to appeal to conspiracy theorists.



https://www.bea.aero/uploads/tx_elydbrapports/f-sc000725a.pdf


For example: The maximum take-off weight was possibly! exceeded on this flight by a few hundred kg. But that is not enough to explain the crash. And it does tell little about past take-off weights.



Same for the resulting off-balance CG - exceeded CG sounds impressive, but it was 54.25% in the end, with 54% being demanded for a normal take off and 54.25% being the aft limit for a maximum performance take-off.



Both nothing that causes a fire.



(And after all - the fire and leaking fuel did correct the overweight situation quickly)

 

[APDAF]

This might be very significant, Boeing is cutting back production of the 737 MAX.

https://www.bbc.co.uk/news/business-47834556

 

[Evil_Onyx]

My information comes from this interview and several books on the Concorde.

True he does embellish abit, but he was a Concorde pilot and would know the flight characteristics and procedures better than most.

Remember that Concorde is a pure Delta and was trimmed by fuel transfer. The over weight issue and loss of power in a critical point in the flight meant the pilots did not have sufficient energy to climb and stabilize aircraft.

From : https://reports.aviation-safety.net/2000/20000725-0_CONC_F-BTSC.pdf same report different hosting.
It had 874kg more baggage onboard than recorded by the dispatcher (not in data sheet given to flight crew) it was also loaded aft of the calculated CG.

Max Takeoff weight in manual 185070kg actual weight from report 185757kg - 186251kg (based on passenger weight averages). So still over weight by between 687 and 1181 kg.

The report states that the tanks where overfilled. part 6.3

All these factors still makes it a multi point failure, overweight, overfilled fuel tanks, time pressure and failure to identify a pattern in tire failures as dangerous.

I was in error on the FE shutting down the engine with out telling the pilots. He told them after he had done it.

---------- Post added at 22:48 ---------- Previous post was at 22:34 ----------

Also the Ignition source was never identified, only theorized to be a short in the Gear bay. The engines reheat was eliminated as a source during the investigation.

 

[MaverickSawyer]

This might be very significant, Boeing is cutting back production of the 737 MAX.

https://www.bbc.co.uk/news/business-47834556

:lol:

And they had pushed so hard to reach their current rate of more than 50 airframes a month...

 

[Urwumpe]

The problem with the overfilled argumentation:

Before the accident flight, the top up with Jet A1 fuel had been completed at around 13 h 55. An overfill of 300 litres corresponding to a quantity of 237 kg had been added. According to witness statements, this overfill was performed on tanks 1, 2, 3 and 4. The short duration of the wait and the temperature at that moment in time means that it can be considered that there was no significant change in the volume of the fuel before the takeoff. The fuel loader’s filling order shows a loaded fuel weight of 94,800 kg.

But tank 5 was the one that ruptured, it was at 94% of its capacity. Its the only tank of which debris was located on the runway.

Also, if you read the report carefully there, overfilling was a standard procedure that allowed to load 1630 liters extra.

Same with the ignition sources - the investigators did consider that but:

Forward propagation of the flame via the outside of the nacelle meets a theoretical obstacle: the propagation speed of a turbulent flame can barely exceed a few metres per second whereas the airstream under the wing of the aircraft is about 100 m/s. It is, however, sufficient for the flame to encounter locally, at a given moment, airflow that is sufficiently slow for it to be able to flow back. The complex geometry of Concorde’s lower wing, in particular the presence of a fairing between the nacelle and the wing, the disturbance to the airstream by the presence of the flame itself and the wake from the landing gear are three elements which make it possible to envisage sufficiently low speeds to be born by the flame

Note 1: Because of the chaotic nature of the turbulent combustion, a numerical simulation would be too inconclusive since the results would be too dependent on the model and the hypotheses selected. Flame forward propagation from the rear of the aircraft could not be produced during the tests conducted in Great Britain, but it was not possible to reproduce the exact conditions of the accident.

 

[MaverickSawyer]

Back on topic... Saw a report about an issue with the horizontal stabilizer design of the 737 that's been known about since the days of the 737-200... If the stab is sufficiently nose down and the crew is pulling back hard on the yokes, the forces generated are sufficient to prevent the crew from manually trimming the stab. The crew may well have run into this issue, which may be why they repowered the trim motor.

 

[Urwumpe]

Back on topic... Saw a report about an issue with the horizontal stabilizer design of the 737 that's been known about since the days of the 737-200... If the stab is sufficiently nose down and the crew is pulling back hard on the yokes, the forces generated are sufficient to prevent the crew from manually trimming the stab. The crew may well have run into this issue, which may be why they repowered the trim motor.

Makes sense, the elevators could act like a trim tab, if the plane is sufficiently fast it could create a lot of torque that way. And if I am not thinking wrong there, it makes sense to prefer the moment by elevator oppose the torque on the aircraft generated that way, so a "nose up" by the aircraft means a "nose down" rotation by the stabilizer, since a completely moment-neutral aerodynamic should be impossible for all velocities.

 

[MaverickSawyer]

Makes sense, the elevators could act like a trim tab, if the plane is sufficiently fast it could create a lot of torque that way. And if I am not thinking wrong there, it makes sense to prefer the moment by elevator oppose the torque on the aircraft generated that way, so a "nose up" by the aircraft means a "nose down" rotation by the stabilizer, since a completely moment-neutral aerodynamic should be impossible for all velocities.

Exactly. It gets turned into a stabilator, like ona Piper Cherokee, iirc. You, the pilot, control essentially a servo tab on the trailing edge, which then "flies" the all-moving stabilizer/elevator.

 

[Urwumpe]

Exactly. It gets turned into a stabilator, like ona Piper Cherokee, iirc. You, the pilot, control essentially a servo tab on the trailing edge, which then "flies" the all-moving stabilizer/elevator.

Its similar on many ships that move a small trim tab instead of the whole rudder for controlling the rudder angle. But that is no solution for every situation.

 

[Cras]

Just a side note about your questions on why they bothered selecting altitudes and headings in the MCP during such a mess. These actions are not only commands for the autoflight system, they also give inputs to the pilot for his altitude and heading ajdustments while he is flying manually (the altitude-speed-heading commands on the MCP are reflected on the primary flight display and navigation display). This is routinely done regardless the fact that the autpilot is engeged or not.
I agree with you that in such a situtation these actions were not a priority and maybe also distracting

any use of the MCP/FCP is a minimal distraction and is commanded in SOPs for even the most critical of moments, such as a V1 cut. Either use it or turn the flight director off. last thing you want is to leave it on and have it give you commands to do something you dont want to do.

 

[C3PO]

Its similar on many ships that move a small trim tab instead of the whole rudder for controlling the rudder angle. But that is no solution for every situation.

I don't think servo- or trim tabs are used on ship rudders. It's much easier to put the rudder axis closer to the center of pressure.

Becker flap rudders have sort of "flaps" to increase efficiency (especially at large deflection/slow speed). But those work in the opposite direction to servo tabs.

The only servo flaps I've seen on ships are on wind rudders for smaller sailboats.

Large scale RC planes often use boost tabs, and I believe that the DC-9 used manually operated servo tabs on the elevator. The usual joke was that DC stood for "Direct Cable".

 

[Urwumpe]

I don't think servo- or trim tabs are used on ship rudders. It's much easier to put the rudder axis closer to the center of pressure.

Assuming you have a ship that is constantly steaming at the same velocity and power setting.

 

[Linguofreak]

Myself, I'd always assumed that there was enough weight budget for heavy machinery that most ship rudders were just rotated against hydrodynamic forces by brute force.

 

[C3PO]

Assuming you have a ship that is constantly steaming at the same velocity and power setting.

You don't need to balance the forces perfectly. If you place some of the rudder area in front of the axis, it will lower the power output needed in the steering gear.

Myself, I'd always assumed that there was enough weight budget for heavy machinery that most ship rudders were just rotated against hydrodynamic forces by brute force.

Exactly! Furthermore, the maintenance cost of underwater moving parts is very high. Flap rudders were always rare, and have allmost been completely replaced by azimuth drives.

 

[Urwumpe]

Funny - while the trim tab in literature is often mentioned to be used on ships, it seems they have never been common.

All I can find are flap rudders like the Becker rudder, which really are common for coastal ships.

The Queen Mary is mentioned in the Buckminster Fully quote, but it had a classic skeg rudder without a trim tab.

 

[C3PO]

Funny - while the trim tab in literature is often mentioned to be used on ships, it seems they have never been common.

We used to call them Sex-in-a-hammock-ideas.
It's a good idea in theory, but in reality almost totally impractical. :lol:

 

[Urwumpe]

We used to call them Sex-in-a-hammock-ideas.
It's a good idea in theory, but in reality almost totally impractical. :lol:

The only great use of a trim tab on a ship seems to be a mechanic autopilot for cruising yachts... no surprising considering the available forces. But that looks like a DIY solution right now.

 

[C3PO]

The only great use of a trim tab on a ship seems to be a mechanic autopilot for cruising yachts... no surprising considering the available forces. But that looks like a DIY solution right now.

Yes. Those wind autopilots have all the complexity above water.

There are several models on the market.

(Wow! How did we this far off-topic again?) :lol:

 

[Urwumpe]

Back to topic - looks like our discussion here was not too far off the reality:

https://www.seattletimes.com/busine...-737-max-may-have-failed-on-ethiopian-flight/

Looks really like the hypothesis, that the aerodynamic forces caused by elevator up and high speeds made it impossible to trim mechanically to ANU, can hold water.