Over Boost on Takeoff

nickrahal@gmail.com

Turbo Over-boost
My 1981 PA32R-301T SP (IO540 S1AD) on takeoff and with the throttle full forward gives an over boost indication. I end up fumbling with the throttle until the over boost light goes out, which is obviously distracting. Takeoff is the only phase of flight this happens. Is this common? How much tolerance does the engine have to over boost? Thanks

Scott Sherer

Those of us with turbo engines do this on occasion. I did it last week in my turbo-arrow. If it's only a few seconds, don't sweat it but don't make a habit out of it! Do you have a fixed waste gate or a variable waste gate? Just curious.

nickrahal@gmail.com

I’m not sure.

I was listening to a Mike Busch podcast on leaning procedures. He mentioned that over boost is common during takeoff, especially if the engine oil is not at operating temperature and will correct itself without pilot action. But that’s in contradiction with the operating manual which says even short over boost can do substantial damage to the engine.

Scott Sherer

Don't wait for the engine to correct itself. Take action immediately and pull the throttle back to a safe level.

nickrahal@gmail.com

Yes....I never over boost more than a second or two

Scott Sherer

You're fine. Don't forget there's a blow-off valve in your exhaust to take care of this...

Tmccall

I set the throttle lever to a pre determined spot on the quadrant that gives me the number I want. I have an intercooler so I use 33. In my case, it’s the middle of the “R” on the quadrant. Its very close once you find the position. I make minor adjustments once I am stabilized in the limb. Just a technique.

nickrahal@gmail.com

Thanks for the input!

Brad75089

It has been my experience that you never go full throttle on a Turbo aircraft. I have a Turbo Arrow and the OVERBOOST light comes on at 41". I start my roll easing the throttle forward until I get to 39". I leave it there until I start crosswind, then reduce it to 35". Some turbo aircraft have a fixed wastegate, with these, I would take it up to 35" and then let the turbo spool up and then ease into 39" for climb.

nickrahal@gmail.com

Thanks. Another question: my turbo's redline is 36 inches and it is supposed to be able to maintain 36 inches until critical altitude (16,000 +/_ 500 ft)per the maintenance manual.

In a test this weekend the MAP started to decrease below 36" at 8,000 ft and could hardly maintain 27" at 16,000 ft. Is this normal or is there a problem?

Scott Sherer

Sounds like a turbo charger / wastegate issue. It's time to have your A&P look at it.