In this week’s FFAREX a report on a DR400/180 suffering carb icing in cruise.
Strong humidity and temperature around 10°C. It occurred in the Macon area on a flight from Lyon Bron to St Cyr.
gallois wrote:
if I can find an old TT/PPL “manuel de vol” I’ll see what it says and post it if I can.
If it can help, I have the excellent Zilio book here, I can scan a page and post it here if you wish.
BTW, I don’t believe this depiction of carb ice to be accurate. If the ice accumulation was so severe as to block the inlet tract and cover the throttle plate as shown, the throttle plate/shaft would stick in position or wouldn’t fully close – which does not seem to be the case. It also wouldn’t melt and clear immediately when carb heat is applied as is often the case.
@Silvaire don’t you live in quite a dry climate?
I am based at an airport in a dry climate, but the conditions can vary between airports I use in the local area, and with time of day. As I write this in the morning, ATIS reports a 1 C spread between temp and dew point at my base. Regardless, I don’t use carb heat on most approaches with my Lycoming. The AFM specifies use “as required” and as with most Lycoming installations I’ve found that carb ice is possible, but not a common occurrence in my use. In contrast the small Continental I flew previously was reputed to be an ice maker and I used carb heat profusely.
@maxbc if I can find an old TT/PPL “manuel de vol” I’ll see what it says and post it if I can. I seem to remember it being much like the picture you posted.I don’t think 4 stroke Rotaxes were around back then. Let alone in certified machines.🙂
The alternatives to Lycoming or Continental IIRC, and mostly for the likes of homebuilt, were, Limbach/VW and JPX and I really can’t remember what the carb/throttle heat situation is.
Certified (DA20). The training insists substantially on it (the BEA diagram in OP is also in the official PPL theory handbook and there are questions about it in the exam).
I’ve been trained (with actual anecdotes I believe, but it’s already been more than a year) to be aware of icing before completely freezing the engine and having to glide to higher temps (hopefully) and wait for ice to melt by itself (hopefully before being on the ground). Whether ice forms on the fuel nozzle itself or in the throttle, I’m not sure.
This image corresponds to my training, and is the first picture (from wikipedia) that pops when googling it. It shows the ice does not form on the carburetor itself but rather the tube after the fuel vaporizer and on the throttle valve itself (because of the high venturi effect).
That’s interesting. Is that a 912 in a certified aircraft? On the 912 in the Super Guépard there isn’t any carb or throttle (obviously a term change since I did my TT, now known as PPL) heat mechanism and so far no icing problems.
In the French PPL material, carb icing is instead depicted as throttle icing (it happens especially when the throttle is low which creates an additional venturi tube after the carb). When using carb heat the engine can run rough for a few seconds (and it feels like successive blocks of ice are being swallowed by the engine). I suspect in more extreme cases it could be longer, and AFAIR you can lock the entire pipe with ice (at which point you have to wait until it melts by itself). Although this (fortunately) never happened to me, I sometimes need to apply carb heat several times in order to fully get rid of the ice (with a 912).
@Silvaire don’t you live in quite a dry climate?
I live in an area much of which was reclaimed from the sea by Dutch engineers back in the16th century. Known as the Venise Vert there are said to be some 75,000 km of canals criss crossing the area. So you can imagine this area is quite humid.🙂 and as such carb icing is something we are all very aware of here.
On the Rotax 912 we have at the club the carb is always in a flow of heat because of its positioning. The UK LAA still made it necessary for Rotax engines to also have carb heat added in order to gain a permit.
