Broken carb cable

[wombat13]

Turned up for a landaway yesterday afternoon in the club PA28 - visiting Barrow for the first time. Phoned them before I left. 25kts gusting to 30 was a tad too sporting so I planned to turn o/h Fleetwood and come back to the field.

For the first time since I qualified, my excitement at the flight marginally exceeded my anxiety. Looking forward to a good flight.

During the initial carb heat check (1200 rpm) there was no drop. It caught my attention. During the power checks there was also no movement. I really wanted to make this flight. But to do so would be stupid.

Close down. As luck would have it two engineers were working on a 152 beside me. Ten minutes later they have the hood off. Five seconds to make the assessment. The carb heater cable has snapped. I look up at the sky - perfect conditions for icing. I would be going nowhere in it and they would have to order a cable which would take a day or so.

Was it me on the initial check? Too rough? I don't believe so. I have come to treat all parts of the aircraft gently during start-up and thereafter.

I found the guy who flew it before me and asked him did he notice anything? "No" was the response. If I was to put money on it I would say the problem existed before I got into the aircraft.

The lesson? Makes sure you do your checks. Make sure you are looking for what should happen and don't just consider it done because you have crossed it off your list. Should you be flying, during the FREDA watch for the drop. If it does not come, you should have a clear plan in your head for what you will do in the event. There is nothing like the aviation Gods looking down on you and deciding to teach you this lesson when you are sitting in a field in Shropshire and not in the Manchester low level corridor at 900 ft when the engine is running rough. Thanks to whoever up there took the curve out of that particular curve ball.

Happy flying. The Wombat

[bcfc]

Good catch! - and another drop from the cup of luck into the cup of experience.

The carby cable broke on me once, but no doubt then - came completely out in my hand. Somewhat irritatingly, I had to move 3 other aircraft out of the way in the hanger to get mine out which took ages, only to then have to put it back. :{

[Yorks.ppl]

I wonder if the carb heat cable would tend to fail safe? in other words is it most likely to fail when it reaches the fully closed position. (or should that be fully open, in any case carb heat on is what I mean) That would certainly be the best outcome if in the air.

[Holdposition]

wombat13

Club aircraft? wasn't GU??T by any chance?

[Whirlybird]

I had the same thing happen as a very new student. The instructor flatly refused to fly, despite my pleas - I didn't know any better at the time - that would it really matter, it was a nice sunny day, etc. A good learning experience for me.

I also had alternator failure when on a dual cross country with an instructor. We just turned off all necessary electrics and flew home, no hassle.

We had a spider in the pitot tube recently. We found it before flight, and and went no further than to maintenance. Now I'm always super-careful to check my ASI is working before takeoff; sometimes I even taxi a little fast to check it, if I have the opportunity.

The good thing about these sort of incidents, especially if you've got someone more experienced with you, or they happen on the ground, is that you never ever forget what to do if they happen, or what to check to make sure they don't. And you stop believing that it won't happen to you!

[Mike Cross]

I wonder if the carb heat cable would tend to fail safe?
MMmmmm....... Didn't know one position was safe and the other unsafe.

Perhaps you should tell someone, then we could all remove the controls and leave them permanently fixed in the "safe" position!:p

I wouldn't rely on it ending up in either position. Without the cable to hold it there's not telling where vibration and airflow would leave it.

Mike

[Windy Militant]

Perhaps you should tell someone, then we could all remove the controls and leave them permanently fixed in the "safe" position!

I believe that's what the RAF did with the Gypsy Major engines on their Chipmunks.
The carb heat was wired permanantly ON. ;)

[Yorks.ppl]

Mike Cross,

If I were flying along in icing conditions I reckon that carb heat stuck on would be significantly safer than carb heat off dont you?

I wasnt suggesting it, or any other control should be permenantly fixed, where did you get that idea from?

I was simply wondering if the aircraft was designed to fail in the safest way which would seem to be sensible to me.

[Mariner9]

IMHO blooming ridiculous in this day and age that we're still flying round with carbs susceptible to icing

[Brooklands]

IMHO blooming ridiculous in this day and age that we're still flying round with carbs susceptible to icing
Yes, I agree. All the new 172s are fitted with fuel injected engines. I just don't understand why Piper stil fit carburetted engines in the new PA-28s

Brooklands

[sunday driver]

If I were flying along in icing conditions I reckon that carb heat stuck on would be significantly safer than carb heat off dont you?

. . . and if you were 2/3 down the runway and still only doing 50% of Vs . . . ? :uhoh:


SD

[FlyingForFun]

. . . and if you were 2/3 down the runway and still only doing 50% of Vs . . . ? Do cables generally fail when you're on the runway and not moving the controls? My experience (of aeroplanes and cars) is that cables tend to fail when you move them. In the case of carb heat, if you're moving the carb heat lever it would almost certainly be a safe time for carb heat to be on, so I can see sense in Yorks' suggestion.

On a more general note about failures and noting them at pre-flight checks, I was doing a currency check (or was it a type conversion, I can't remember and it doesn't matter) with an ex-student of mine recently. We got to the holding point, checked the mags, and found no drop on the left mag. Taxied back in and took the aircraft directly to engineering.

Afterwards, someone said to my ex-student "you must be gutted, beautiful weather like this and you can't fly because the mag's broken."

"No," he replied. "Actually, I'm really pleased with myself. I always do those checks at the holding point, and nothing significant has ever happened. I'm really pleased that the first time something interesting happened, I noticed it!" Well done - exactly the right attitude.

FFF
-------------

[TheKentishFledgling]

Was it me on the initial check? Too rough? I don't believe so.

Doesn't overly matter if it was you - you made a good (and correct) decision NOT to fly if something was bothering you.

Good call IMHO :ok:

tKF

[Yankee]

One reason carb heat cables and mixture cables tend to break is because they are set up with bounce in them. That is to say that when they are in the fully cold or full rich position the knob in the cockpit is not flush against the panel. This is to ensure that you reach the full stop position before the cable reaches its full travel, if you see what I mean. Now pilots seeing this think that it should be flush and may be think it keeps backing out, so what do they do, as they have never been told this before, they keep pushing it back in against the panel. This causes the piano wire to keep bending against the full stop position and if you keep bending a wire it breaks.

Just my two-penny worth.

[Final 3 Greens]

sometimes I even taxi a little fast to check it What about your airspeed alive check on the take off roll? Don't you also cross check speed against a decision point whilst the accelerate-stop equation still works? (For the pedants, I know that this is only published for multi engine aircraft, but the principle is the same)

[Whirlybird]

What about your airspeed alive check on the take off roll?

Yes, of course I check it then. But at Sleap, I have to taxi a long way from where the aircraft lives to get fuel etc. So if it's safe, I try to check it then too. Why not, if I can? Then if anything might be wrong, maybe I have advance warning, before I even consider taking off. It's just me, and just a belt and braces approach. I've only been that extra-careful since we had the spider in the pitot tube.

[Yorks.ppl]

. . . and if you were 2/3 down the runway and still only doing 50% of Vs . . .

Why would I be in such a position?
If the carb heat had failed in the on position I would have noted that there was no rpm drop during power checks carried out 30 seconds previously and therefore would have elected not to try to take off.

[Mike Cross]

Yorks ppl

Sorry the attempt at humour fell flat. I agree that a failure to the hot air position would be preferable to the cold however in my experience that is not the way the things are designed.

We've had reliable fuel injection in cars for donkeys years, which gets rid of the problem entirely, but then if I were driving a 57 year old car instead of a 57 year old aeroplane I wouldn't have it on that either.

All engines are different. For example the small Continentals have all of their inlet manifolding hanging out in the breeze, making them more susceptible to carb icing while the Lycomings tend to have it embedded in the sump where it gets warmed by the oil.

While the RAF ran their Chippies on permanent hot air they no doubt also factored the result into their take-off calculations. Running other engines on permanent hot air might not be a good idea because it causes them to run rich and, as a result, cooler, making them not only less efficient but also increasing fuel consumption and the environmental impact.

There are a number of situations after take-off where inability to achieve full power could be an issue, for example clearing obstacles following an enforced go-around or countering down-drafts in the lee of hills. However the likelyhood of that happening on a flight where the carb heat control failed after the pre-take-off checks is insignificant enough for me not to worry about it.

Mike

[Yorks.ppl]

seems its all down to luck then, these things always seem strange in such a safety concious industry. A simple spring would be all that was needed to ensure that it failed in the on position.

Mike Cross, sorry also if I had a humour bypass yesterday:ok:

[shortstripper]

Of course if it failed in the cold position you could always fly at full throttle until safely over the airfield. Carbs rarely ice up at full power.

SS