Diamond DA-20C1 mistrim led to accident

[pelmet]

"A13W0075: A Diamond DA 20-C1 Katana had been rented for a flight to High River, AB and return. Prior to take-off from Springbank the pilot observed that the trim position display was unlit, and following take-off the pilot was unable to operate the electric elevator trim. The trim appeared to be jammed in the full nose up position, as high forward stick force was required to maintain a normal pitch attitude. The pilot elected to return immediately to the airport and during the landing the aircraft bounced and began to porpoise. The nose wheel separated from the nose gear strut and both propeller blades struck the runway prior to the aircraft coming to a stop. The pilot was the sole occupant and was uninjured. The nose gear, propeller and lower engine cowl sustained damage. Initial maintenance examination found the elevator trim circuit breaker disengaged. The circuit breaker was re-engaged and the trim system was operated several times through full travel with no fault found."

A quick question.... Going from memory there are trimming the aircraft adjusts spring pressure on the elevator. But there is a tab on the elevator. Would it be possible on the walkaround to see a trim setting that was full scale?

[DanWEC]

I don't remember the actual trim tab position being specifically checked as neutral on the walk around, but the led position is set to neutral when the master goes on, and I'd bet a full down tab is something that would definately look different if you saw it after a few walkarounds under your belt.

This accident sucks. So much wrong with it. Why wouldn't the pilot play with the trim on the walk around if he saw the indicator led's out? Get Mx to take a look? Checklist states it should be neutral for walkaround, and takeoff. Missed those. Breakers should get checked at least twice before takeoff, missed all those. Trim isn't too hard to overcome in a Katana while landing, but I guess it might be very awkward for a student.

I guarantee the previous flight was a training flight where the instructor gave a trim runaway emergency then forgot to reset the breaker.

Not to speculate, but just a goat dance all around.

[Oxi]

"A quick question.... Going from memory there are trimming the aircraft adjusts spring pressure on the elevator. But there is a tab on the elevator. Would it be possible on the walkaround to see a trim setting that was full scale?

The switch controls an electrical actuator beside the vertical push rod in the vertical stabilizer. The actuator applies a load to compression springs on the elevator pushrod.

With that said the you would feel some stick pressure if it was trimmed either direction to the full travel stops when doing a control check. The indicator will also indicate which ever position it has been set to, its fairly typical for the FTU aircraft to have some of these lights burned out.

If the previous flight was with an instructor, good on he/she to actually let the student take the runaway trim all the way to landing and taxi off. I find it hard that they wouldn't debrief the scenario and reset the CB if this was the case.

I would hazard that the previous flight used the trim significantly on final approach and gave it a nose up attitude, lights are burned out and the next student failed to check.

oxi

[PilotDAR]

I had a very serious trim problem in a Cessna 206, which resulted in huge pitch control forces. I estimate a 50 pound push was required to maintain level flight. Very tiring to fly and land, but I succeeded. A wise trick I was told after the fact ('wish I'd though of it at the time) is to allow the aircraft to enter a turn as tight as you need, which will balance off the pitching up force. I'll give you time to figure it out, rather than taking the first option, which might not be the best.

That said, aircraft which do not have mechanical trim (I know nothing of DA-20s) is required to be flyable with the trim stuck at either extreme. I would think this should be briefed as a characteristic of the type during training. I flew the SM 1019, which seemed to have only electric trim (which always worked ). I was not trained to know that the aircraft did have a secondary manual trim wheel, but it was not placarded, and was hidden behind a velcro'd upholstery panel. I should have researched that more, as my check pilot did not know about it either!

[Rookie50]

No mechanical backup?

[DanWEC]

Fighting the full trim force, (which I actually measured once with a digital scale for a nearby college building a simulator) if I can recall was about 20 lbs. Pretty light. I'm willing to guess that they determined there wouldn't be a need for a mechanical wheel given that- but only a guess.

[xysn]

"A13W0075: [...]Prior to take-off from Springbank the pilot observed that the trim position display was unlit, and following take-off the pilot was unable to operate the electric elevator trim.

I have flown the A1 version of these things. The trim position indicator is a stack of discrete LEDs. My experience is that sometimes the trim position is "between" the position indicated by the LEDs and so none of them light up. (The "neutral" position, oddly, is sometimes "between" positions indicated by the LEDs.)

A quick press of the trim button up or down would usually light up one of LEDs.

Perhaps the pilot assumed that that the trim was roughly neutral and did not check to see that the trim system was indeed working.

[pelmet]

What is the tab on the elevator for in the C1. Is it an anti-servo tab?

[Trematode]

What is the tab on the elevator for in the C1. Is it an anti-servo tab?

It's just a ground-adjustable fixed-in-flight trim tab, if I remember right. The Pilot-controlled mechanism uses an electric motor to spring load the elevator for the desired trim forces. The Da40 and 42 make use of more traditional pilot adjustable trim tabs for inflight trimming (mechanical wheel, with electric trim option).

Don't know what this guy was thinking as checking the trim function should have been part of the pre-flight inspection, with a second check of the indicator prior to take off that should have been part of the undoubtedly long-winded and bloated FTU checklist! As someone else said, I'm pretty sure the position of the stick in the cockpit would have been noticeably different enough to be another hint of a mistrim to those accustomed to flying the plane regularly.

[pelmet]

What is the tab on the elevator for in the C1. Is it an anti-servo tab?

It's just a ground-adjustable fixed-in-flight trim tab, if I remember right. The Pilot-controlled mechanism uses an electric motor to spring load the elevator for the desired trim forces. The Da40 and 42 make use of more traditional pilot adjustable trim tabs for inflight trimming (mechanical wheel, with electric trim option).

Maybe. Never seen a fixed tab for an elevator before.

As someone else said, I'm pretty sure the position of the stick in the cockpit would have been noticeably different enough to be another hint of a mistrim to those accustomed to flying the plane regularly.

I suppose that makes sense. Increased spring pressure on the elevator actuating mechanism is the reason the stick moves when you adjust trim.