I’m not familiar enough with the C150, how does the carb heat work? If it’s getting its heat from the engine, can it be efficient if turned on after the engine quit?
Very good point on the mags.
When carb heat is on, the intake air gets ducted over the exhaust stack which would still be warm.
What is strange is that you experienced a sudden stop. The RPM should have degraded before. In a 182 it’s harder to notice because of the governor. The best indicator is the airspeed there.
Achimha it was 15 years ago and I do not remember if it made any sign beforehand but for sure I did not spot it.
What I remember is that I had considerably reduced RPM for the descent and suddenly it stopped igniting without warning.
You are right that the exhaust should still be a bit warm but I guess there’s not much time left there.
All you are relying on at that point in time is residual heat coming from the engine and not heat from combustion gases.
denopa indeed (I assume) if you let the exhaust cool with an non igniting engine then you shall not get much heat out of it to send to the carburetor except of the one I mention above to Achimha.
So if I had in mind to pull the CH knob it was a wrong sequencing to leave the checks second and do the ditching preparation first.
The problem is that all these years (and even that day right after the incident) I cannot remember when and if I pulled CH.
Oh wow Petakas, great write up and thanks for posting.
Just like Robert I also thought you had run out of fuel as one tank might have been sucking fuel out of the other! I’m not surprised you didn’t think about carb icing…
I’m not an expert on 172s, but can this actually happen when you’ve selected one tank or is it one of those flying myths?
I have to say if I had to choose somewhere to ditch, the Med would probably be it. Did you think oh well, might as well swim the last couple of miles?
Did you think oh well, might as well swim the last couple of miles?
LOL! nope, the sea at the Marathon bay may have been calm that day with water temps around 15*C for that period but I for sure I was not relying on swimming to shore, that is why I made sure someone knew a.s.a.p. that I was about to ditch.
If your C172 sucks fuel out of a wing and tosses it overboard via the other, then something is seriously broken and the aircraft is not airworthy. The connected fuel system needs to be correctly aligned and not many shops know how to do that well even though it is spelled out in great detail in the maintenance manual. There really is no reason to fly a 100 series Cessna with the fuel selector not set to BOTH. Ok, there are a few involving different types of fuel in each wing but I will not go into details
Susceptibility to carb ice is highly installation dependent. Like in petakas’ case, a rental plane is the one you should be aware of. My C172M would only show carb icing in rather extreme situations and my TR182 does not do carb icing at all, even though it is an IFR tourer. I have a carb temperature gauge but it is hardly ever near the yellow arc because of the turbocharger heating up the intake and the carb being located at a nice and cozy place. I know of a pilot in a rented C182 who almost had the same experience as petakas but over the Channel and he didn’t notice it because the C182 has a prop governor keeping the RPM fixed. Only by coincidence he noticed the airspeed dropped by 20 KIAS.
That is a real heart stopping experience – thanks for posting!
I’ve never flown a rental-type plane in which the fuel gauges were other than useless.
I have read somewhere that a common thing, in fuel exhaustion incidents, is that one runs #1 tank empty (in error, not watching the fuel status, etc), switches to #2 tank, nothing happens for a bit (because it takes some tens of seconds for the fuel to start flowing), so one switches back to #1 tank, then a bit of the fuel from #2 tank comes through and the engine briefly bursts into life, then stops, but the pilot interprets this as there being fuel in #1 tank and leaves the selector on #1, and starts looking around for a different cause, but of course the engine never restarts because #1 is empty.
Here is a link on uneven fuel flow in SE Cessnas, not relevant to the incident described but hopefully useful
If the RPM (for fixed-pitch props) or MP (for variable-pitch props) drops to the bottom of the green arc, carb heat comes on, whether it’s because I’m closing the throttle or because carb ice is doing it for me. That way it’s an automatic response to a parameter that’s part of the scan anyway. One of the workload-reducing tricks I got from my instructor.
Interesting read Robert.
Never thought that venting a fuel tank could be such an engineering headache! I finally know the history of why the fuel tanks on the 152 have little holes in them.