Vilnius crash

[Alistair_Heaton]

EC-MFE 737-400 Crashed on Approach

19 Oct 2015 - The Lithuanian AIB have issued an interim report into the 737-400, EC-MFE, operated by Switftair, which crashed on approach at at Vilnius, Lithuania.

www.b737.org.uk

Prelim report out.

Human error, apparently this error has been occuring for decades through all the 737 series. Never been fixed.

 

[LittleInch]

How did it crash if the A hyd pumps are still on?

 

[TugboatEng]

The leading edge slats retract when the B hydraulic pumps are turned off. The flaps were not extended. The plane stalled.

 

[Garbage1]

 

[LittleInch]

So a and b are two separate systems which don't inter connect? That's not intuitive.

From the excellent b737 site http://www.b737.org.uk/hydraulics.htm

There are some automatic and manual cross connection between the two systems, but it looks rather complex all right.

 

[MintJulep]

In the moments before they were switched off there were calls for the engine anti ice to be used. This strongly suggests that the hydraulic pumps were mistakenly switched off instead of the engine anti ice switches.

I don't follow.

Up is off, down is on for both sets of switches.

I'd guess that convention is applied for all switches.

If so, I'd expect that to be ingrained. How do you mistakenly turn a system off when you're intending to turn something on.

 

[LittleInch]

I guess he just thought to move them to a different position than they were to start with....

There are a whole bunch of very similar switches and some will normally be on and others off.

It is a pretty big error, but the fact that only kne hydraulic system runs the flaps is a bit single point failure and it would seem there is no feedback that the flaps weren't moving when commanded?

 

[MintJulep]

If we believe your earlier link, then I don't see any hydraulic backup for TE flaps.

I guess the mitigation is "you'll be landing fast, deal with it."

From the excellent b737 site http://www.b737.org.uk/hydraulics.htm

 

[LittleInch]

That seems to be the case. There are some cross over elements, but the "power transfer unit" seems toexostfor the LE flaps only. It's not clear if its on,y to retract them or extend them, but the TEflaps are system B only by the look of it.

Apparently that rrrr rrrr rrrr noise you sometimes hear after landing when they are retracting the flaps is that PTU working when they've only one engine or one is at idle. Apparently.

 

[Alistair_Heaton]

Now go have a look at the MAX and see if the same situation exists

 

[LittleInch]

From what I can see the hydraulic system for the MAX is basically unchanged from the NG.

So you really don't want to lose your no 2 engine by the look of it.... There is an electric pump but it is lower capacity.

There are some elements of standby and crossover, but I think to would take you a good few minutes to work it out and the standby / third system is pretty low of fluid power. I don't think anything other than system B runs the trailing edge flaps.

 

[Alistair_Heaton]

I would be amazed if it's changed since the original 737 from the 60's

If it had it would have triggered a requirement for a different type rating.

The NG manage to escape a raft of certification changes by a matter of weeks. And if the system hasn't been touched then it will be the same on the max.

Surprised there isn't guards over the hydraulic switches. I am pretty sure the hydraulic kill buttons had them on the Jetstream and the Q400.

 

[TugboatEng]

You know what they say, doubling redundancy doubles the chance of a failure.

 

[IRstuff]

it would seem there is no feedback that the flaps weren't moving when commanded?

The flap position was recorded in the FDR, so that reflects some indicator in the cockpit, which the pilot(s) apparently didn't check, particularly when specifically asked about it.

 

[Alistair_Heaton]

I seem to remember it's a not very noticeable 1" diameter dial next to the gear handle.

The A220 flap/slat indication also isn't very in your face. Not that it really needs to be as the flap selector handle is easily seen. And if it's not at the selected position it triggers a master caution and tells you.