What can bring down a 421? (OK-TKF)

That is a damning report but, based on some stuff I have heard from “down there” (the country I come from too!) it does not surprise me. One engine shop is known to perform engine overhauls by changing cylinders and painting the crankcase (and of course issuing an EASA-1 ). I hope that questions are asked about who was responsible for the maintenance and who actually did it. On this class of aircraft, the pilot often has no involvement in the maintenance status.

Thanks for posting.

It is good that they found a cause. One still has to wonder if there is no way to control a 421 with a seized, unfeathered LH engine. Drag should be less than an unseized engine, OTOH you would lose one vacuum and one alternator. The live ones should be enough to cope with one prop anti-ice and the basic requirements.
We used to operate a not too dissimilar 402 and it did not have automatic load shedding so I assume unless one switches off antiice on the seized engine you could overload the live alternator.

Ultranomad wrote:

The failure of the left engine had been developing insidiously over a long term, presumably due to the camshaft momentarily seizing on each revolution

In that case one would expect regular oil analysis and filter inspection would catch it.

The Air Accidents Investigation Institute of the Czech Republic released a final investigation report (here, in Czech). In brief: the aircraft impacted the ground in a spin. An analysis of debris showed the left engine to have seized in flight, leaving the prop unfeatherable. The right engine was OK but was either not operating at the moment of impact or operating at idle, which may have been done to recover from the spin. Fuel system was configured to feed the left engine from the right tank and the right engine from the right auxiliary tank, which may have possibly been done by the pilot under the assumption of left engine fuel starvation. The pilot had logged 64 hours of multi-engine time. The aircraft was in private operation and maintained in an, ahem, cavalier manner. In particular, the logbook had records of only 2 annuals over the last 5 years, the avionics did not meet MEL for an IFR flight, and the left engine (GTSIO-520) was 4 years past the calendar limit. The failure of the left engine had been developing insidiously over a long term, presumably due to the camshaft momentarily seizing on each revolution, transmitting the shocks to the gears driving it, wearing out and eventually breaking off the teeth.

Two days ago, I was at an event with numerous pilots and engineers in attendance, and the topic of OK-TKF popped up. One of the guys who flew in the area on the day of the crash said he encountered icing above FL100, which could have possibly triggered TKF’s departure from the normal flight envelope. On the other hand, the same person said he had spun a 421 and a recovery with the normal CofG was a non-event. Make of that what you will.

Pytlak wrote:

Is this normal?

Yes. I must have used a truckload of tissue rolls over the years to clean away all the oil from flaps, gear doors and wing underside that a healthy C421 spits out in normal operation. Mind you, lots of it comes through the exhaust which is two thirds down the engine nacelle and under the wing. As already written in another thread, these engines consume lots and lots of oil when running under power at high temperatures. Almost all of it goes through the exhaust, the engines themselves usually stay clean of oil. 1 – 2 quarts per flight some times, all of which gets deposited on the plane itself…

Rather than looking at the state of maintenance (newish engines have failed on perfectly maintained aircraft…) it would be interesting to see what the pilot’s experience was especially with respect to complex multi-engine planes.

I have a copy of the RAF AP3456 which has a good chapter on spinning, and discusses wing and fuselage loaded spin chararacteristics.

Here is a link to a NASA article that goes into the subject.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19720005341.pdf

Comparing spin characteristics of, say, an Extra (with very straightforward recovery, and relatively neutral between wing and fuselage loading), to a wing loaded 421B with the main fuel in the tip tanks, suggests the 421B will have relatively flat spin characteristics once in fully developed mode. Also with possible rudder blanking, especially with down elevator.

No doubt Cessna will have undertaken some testing, perhaps not at FL140 and asymmetric, but with sheddable ballast and an emergency chute to ensure there is a chance of recovery once the expected flat spin develops.

This link has some interesting comments on the spin recovery requirements for multi engine (none), and work done by the US Army and Beech on the BE-55/58/58P series.

http://apstraining.com/spinning-normal-category-aircraft-what-is-the-risk/

RobertL18C wrote:

A forward CG might aid recovery at the incipient stage, but may not help once autorotation sets in.

Robert, could you please elaborate on this comment? I have always believed that forward CG helps recovery in every phase of a spin, because there is more authority left for the elevator to induce pitch-down moment when you initiate the recovery. In my experience, it is always more effort to recover a spin in tandem aerobatic aircraft with dual occupancy, because the rear CG – and this is the case even after several rotations. Why should forward CG help only in the incipient stage and not when the autorotation fully develops? OK, the rudder authority becomes far more important at the more developed phases, but forward CG still helps to bring both of the wings below critical angle of attack, right?

What was the cause?

Air intake icing (filter)