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Extra 400 (also N121AG loss of control, and autopilot VS mode)

From here

Flyingfish wrote:

The Extra is N-Reg. I bought it as a “refrurbishment project” .
I see you are in LFPN? Maybe you know Amar? he just bought my second hand avionics on behalf of Aeroclub Paris Sud!

.

The Extra looks like quite an impressive plane, although I’ve heard it takes a huge amount of tarmac to get off .

I suspect you bought N121AG, the EA400 that was involved in a very scary loss of control in IMC incident that, thankfully, managed to avoid crashing, just barely.

ps: Yeah, I know Amar and the APS is just 2 hangars over from mine. Unfortunately, I cannot recommend him or the club…

FAA A&P/IA
LFPN

Michael wrote:

The Extra looks like quite an impressive plane, although I’ve heard it takes a huge amount of tarmac to get off .

At my home base we had an EA400 based there, the tarmac available is slightly over 600m, and I never noted that it had any problems getting in and out, as a matter of fact it used less runway to become airborne than an SR20 does. Used to love watching it start and land but it’s recently been sold….

Michael, yes it is N121AG. Can you tell me more about the incident?

Take-off performance:
The E400 has a modest wingspan (11.5 m) and fantastic Fowler flaps. The landing gear is very draggy.
Stall speed is only 58 knots at 2’000 Kg. Vr is 75 knots or so.
The old, rounded tip prop has poor static thrust and is not very efficient in the climb.
So the issue is not the airframe, but the time it takes to accelerate to 75 knots, the high drag of the gear and the poor efficiency of the prop at Vx/Vy. Does a better prop exist? Yes!

Loss of control
I can imagine how this can happen in an aircraft equipped with an STEC55X. Using the vertical speed mode (the E400 can climb at 800 fpm all the way up to the stratosphere), can be a very dangerous idea:
If anything goes wrong that reduces climb performance, the autopilot will gradually pitch up to maintain the selected vertical speed. Whenever the AP runs out of elevator trim OR the plane stalls, the AP will disengage or the pilot will disengage it.
At this point, the plane is potentially stalled with FULL NOSE UP trim. And chances are, the pilot is busy diagnosing the performance issue.
So he pushes the nose down, recovers from the stall, only to stall again as soon as he’s back to level flight.
The pilot of E400 S/N 002 died in such an accident. He recovered from an IMC loss of control, exited under the cloud base, and then lost control again in VMC and crashed. Remarkably, the airframe resisted a 10’000 fpm (!) dive following the initial loss of control.

I will never ever use “vertical speed” mode in a climb. I will establish a certain nose up attitude and have the AP maintain it.

Re aero club/Amar : can you send me a private msg at [email protected]? thanks

Last Edited by Flyingfish at 24 Jan 18:39
LSGG, LFEY, Switzerland

Flyingfish wrote:

I will never ever use “vertical speed” mode in a climb. I will establish a certain nose up attitude and have the AP maintain it.

I must admit I happen to do that when that’s the only AP mode available for climb, but I have to watch the performance like a hawk and progressively adjust the climb rate. When the ROC get down low I fly manually.

I found no incident report about N121AG anywhere…

LFPT, LFPN

The mechanic that used to maintain N121AG at Deurne is a very good friend. The plane had just come out of maintenance and if I remember the story correctly they were over gross, IMC , and climbing out when the pilot lost control, not sure if it was an AP incident or a IA failure, but they are very lucky to have survived. There was an investigation by the authorities, but it was considered pilots’ fault.

Last Edited by Michael at 24 Jan 19:01
FAA A&P/IA
LFPN

Michael wrote:

There was an investigation by the authorities, but it was considered pilots’ fault.

The BEA has no report on N121AG.

Flyingfish wrote:

can imagine how this can happen in an aircraft equipped with an STEC55X. Using the vertical speed mode (the E400 can climb at 800 fpm all the way up to the stratosphere), can be a very dangerous idea:

Absolutely. That is the one bit which most of the legacy AP’s lack: A proper level change mode like IAS hold vs a fixed power setting.

It is usually manageable however, but it needs constant watching. I use the VS climb but always below capability of the airplane (e.g. if it climbs at 800-900 fpm at Vy we use 500 fpm to climb at cruise climb) and always keep the speed under control at 105 mph (Vy is between 85 and 95 mph). Above 10’000 ft we limit AP climb to 300 fpm.

But you are very right, it can be very dangerous if mismanaged. The S-Tec 55x should actually issue a warning when the plane can’t match the selected VS however.

LSZH, Switzerland

When first instructed the AP, I was shown VS mode (for climbs and descents), but soon after reading manual I’ve started using only FLC (flight level change – constant IAS) for climbs, which makes much more sense. I still use VS for descent.

V/S for climb was allways prohibited in the companies for whom I worked, ias/Mach being mandated, pitch under certain conditions.

EGNS

Pete, Noe,

I am with you fully, the trouble is, quite a few legacy AP’s don’t have a IAS/MACH/even Pitch Hold but only VS. The 55x is one of those. It can be used but it has to be used with caution. We found that with our 500 fpm policy it can be used quite safely too. Obviously, while scanning the flight parameters at all times, which is a must anyway.

Any automatisation is only as good as the procedures coming with it. As I found out for myself, knowing how that AP works, what it really does is maybe 20% of learning how to use it to it’s full potential. The rest is devicing procedures to operate it safely.

LSZH, Switzerland

Flyingfish wrote:

If anything goes wrong that reduces climb performance, the autopilot will gradually pitch up to maintain the selected vertical speed. Whenever the AP runs out of elevator trim OR the plane stalls, the AP will disengage or the pilot will disengage it.

Mooney_Driver wrote:

The S-Tec 55x should actually issue a warning when the plane can’t match the selected VS however.

Really?? Doesn’t anyone look at the ASI any more? What happened to the ‘insrument scan’ ? Just let the AP fly them to oblivion?

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