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

Although I have a few hundred hours in C404 and a few tens in C421, I abhor the Cessna fuel systems.

Most of my thousands of MEP hours are in PA23 and PA31, and they both have the simplest of fuel systems, and the PA34 is even simpler. Why is it that Piper could create really simple systems that just, er, feed fuel from any tank to any engine at any time with the minimum of switches, and Cessna had to have these Byzantine systems?

EGKB Biggin Hill

My C310 had that devilish fuel boost set up. It was supposed only to be set to the “armed” setting on full power takeoff and initial climb. There was also a mod or SB that took the pressure switches out of the system, with a checklist change to manually switching to hi in the event of a power failure on takeoff. Crossfeed would only be selected in cruise flight, with the pumps on the low setting or off. But murphy’s law…

Recently, it is quite common that accidents happen to be recorded due to widespread use of smartphones, security cameras etc. This is the case with the C421 accident we are talking about here. The footage showing last few seconds of ill fated OK-TKF were published by one of the Czech TV chanels. It shows the aircraft falling down helplessly in a flat spin and the fireball caused by huge quantity of fuel onboard.

The recording can be seen here:OK-TKF accident

LKHK, Czech Republic

Pytlak wrote:

It shows the aircraft falling down helplessly in a flat spin …

It’s really difficult to see in this video but to me it looks like an inverted spin. This would also explain why the engines were not running.

Last Edited by what_next at 27 Sep 19:05
EDDS - Stuttgart

That’s a flat spin. Wonder how he got himself into that?

Last Edited by AdamFrisch at 27 Sep 19:07

what_next wrote:
It’s really difficult to see in this video but to me it looks like an inverted spin. This would also explain why the engines were not running.

I watched it on a large screen, the aircraft is level and upright, it is a flat spin.

Last Edited by Ben at 27 Sep 19:31

An outcome for normally aspirated twins if the pilot allows allows speed to reduce close to stall asymmetric – Vmc being below the stall at altitude for a NA twin. In a turbo charged 421, assuming the live engine is producing full power, Vmc would be reached before Vs, the departure here being a roll, not a spin. So perhaps the pilot allowed speed to reduce with reduced power asymmetric.

Typical GA twins will have wing loaded spin characteristics, and a 421B with the main fuel in the tips, even more so. Hence a fully developed spin being flatter, and typically not recoverable.

This link has a nice graph showing the relationship of Vmc and Vs to density altitude.

https://www.nashvillecfi.com/multi/vmc.html

Last Edited by RobertL18C at 27 Sep 19:37
Oxford (EGTK), United Kingdom

One engine inop, autopilot on vertical speed, stall and/or vmc roll in imc, game over. Not that one wants to speculate of course…

NeilC
EGPT, LMML

NeilC wrote:

Not that one wants to speculate of course…

No, of course not, but we have nothing else right now. A C421 with 2 people on board, especially if both of them are sitting in the pilot’s seats, is nose heavy. It should not enter a flat spin. So something must have brought their centre of gravity back – either they had heavy cargo in the back or some lighter load shifted backwards.

EDDS - Stuttgart

Is it only the bad quality of the clip which make it look like there is no vertical stabilizer?

LSZH(work) LSZF (GA base), Switzerland
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