In this case leaning and a 200 ft descent rate caused the aircraft to be in danger of passing VNE. Carburettor heat I believe was tried. ATC was very helpful (all this took place in the Lyon areas) so no problem regarding airspace infringements, however mountains and clouds still had to be avoided and a choice had to be made on which airfield to go to (all were ready to accept through ATC). In the end they returned to their home field, rhe decision being made by the instructor after weighing up everything whilst the student flew the plane.
They managed to get to 2000’ AAL and pulled the mixture which cut the engine.
In the FI’s comment section of the report he said that this was the first time that he had experienced a throttle linkage failure in flight and the subsequent default to full power, but had discovered that many aircraft have the same throttle linkages which have not been modified to address this weak spot even though modifications are available.It was for this reason he wondered whether training for this should be part of the PPL alongside power off landings and stalls.
gallois wrote:
which have not been modified to address this weak spot even though modifications are available
Just out of curiosity: What would these modifications do? In case of a broken throttle linkage reverting to full power still seems like the safest failure mode to me, and I would expect all piston engine installations to behave that way. I read that some jet engines get stuck at the last powersetting e.g. in case of certain FADEC failures, but then you still have another engine to work with.
My former flying club had such an incident years ago in a DR400 (coincidence!) with two very experienced pilots on board. A combination of fiddling with mixture and mags, and a long runway did the trick.
Max power is the default failure for variable propellers, the spinner return spring has an easy failure mode, it goes to max RPM and fine pitch on single engines to give max power or climb pitch ( goes to feather and zero RPM on twins mainly to reduce drag)
For turboprops/jets, I guess it is more complicated, you do not max power at sea level takeoff on slow speeds as you will bust max torque limits and you need to maintain min power to avoid engine flameout in high altitudes at high Mach numbers (if you go bellow 40% at FL400 you may have to wait for FL120 before being able to restart 
), in the other hand when landing you don’t want on engine running full power while the other is idle, especially if you are not controlling the one with high power
gallois wrote:
many aircraft have the same throttle linkages which have not been modified to address this weak spot even though modifications are available
Most commonly, and wrongly assembled, is that where the throttle cable terminates at the throttle arm on the carb or fuel injector unit, there is a spherical ball joint, there should also be a penny washer on the correct side of the ball. The reasoning is that if the ball housing wears, it won’t jump off the ball, and disconnect your throttle. So the order from near carb (FIU) to away from is: throttle arm/small washer/ball (of the spherical ball joint in the throttle cable end)small washer, penny (very big) washer/maybe another small washer or two/and castle nut with cotter pin through bolt. If the penny washer is not there, or on the throttle arm side, it’s of no use to save the throttle disconnecting.
I was disappointed to see last summer that my Norwegian friend’s 182 amphibian, which had just had a brand new Continental engine installed, this had been done wrong. Had his ball joint housing worn, it could have jumped off the ball, and caused the disconnect. Other than this failure mode, throttle cables are pretty robust.
Ibra wrote:it goes to max RPM and fine pitch on single engines to give max power or climb pitch
Yes, just because that’s how governors work anyway.
Ibra wrote:
goes to feather and zero RPM on twins mainly to reduce drag
Very engine and system dependant – know your plane! If the plane is equipped with autofeather, then yes. If it’s a standard piston engine in a light twin, the failure mode will be the same as a single.
Ibra wrote:
turboprops/jets, I guess it is more complicated, you do not max power at sea level takeoff on slow speeds as you will bust max torque limits
Yes, or temperature limits. This is very rare, though happened to me with a PT6 once in the early 80’s. I was able to shut the engine down with about one second to spare before it was damaged. Over torque/over temp is easy to do if you’re not paying attention.
Might be worth mentioning that CS propellers on aerobatic aircraft are generally set up to fail to coarse pitch (low RPM and power). This is intended to prevent overspeed in violent maneuvers with the potential for a momentary loss of engine/prop oil pressure.
Another exception is the throttle cable setup on some CV Bing carb equipped Rotax 912 engines. These carbs were originally designed for motorcycle service and accordingly are designed for spring return (closed throttles, low power) if the tension only throttle cable breaks. Changing the carbs to sprung open throttles means using a push-pull cable and linkage setup instead.
On our FADEC-equipped Lycoming, there’s no mixture control nor magnetos, so I would have thought that in good weather / high ceiling, I would use the excess power at full throttle to climb up to 8000/9000 ft where full throttle gives a cruising speed comfortably below Vne; from there on the only option would then to find a field (could also mean – weather and fuel allowing – to fly to a suitable airfield), stop the engines, and orbit down for a forced landing. In bad weather with low ceiling, similarly climb as much as possible, then cutting engine, forced landing.
There was a bit of a debate on this in the LAA mag a couple of years ago, I found it very bizarre that the LAA engineer writing the article thought that a broken throttle cable = throttle closed was best! Yeah, sure it’s the best if it happens on the ground while you’re trying to taxi into your parking spot, but 99% of your time when the engine is actually turning is spent in the air where a sudden loss of power is a lot more unwelcome than a sudden excess of power.
A broken throttle cable resulting in wide open throttle is a much easier to deal with situation than a sudden loss of power. I’d just go over an airfield, call a mayday, turn the fuel off and land on the airfield directly below.
I’ve been told using the mag switches as “blip” switches on modern engines would damage them.
On the first flight after a post-accident rebuild, the throttle wouldn’t retard enough to land, so I pulled the mixture after round-out. I considered trying to do the blipswitch trick to taxi, but got the firemen to push after clearing the runway. Our engineer said it was lucky I’d made that decision.
Maoraigh wrote:
I’ve been told using the mag switches as “blip” switches on modern engines would damage them.
You’d likely get explosions in the exhaust system when you turn the mags back on as fuel-air mixture will keep getting pumped through the engine.
The procedure if you test the ignition in flight and the engine quits on one magneto is to pull the mixture completely, turn the ignition back on and then advance the mixture.
Blipping the mags was the standard method of moderating the output of non-throttled rotaries.
More elaborate systems were developed which interrupted the spark (and possibly fuel, although would unburnt charges be less of a problem with exhaust ports venting directly to atmosphere?) on some of the cylinders to give interim power settings.
The monosoupape on the Sopwith Camel, I believe.
I think I’d be shutting off the fuel from overhead.
