who's stalking now? I probably worked on their autopilots.

Are you referring to the "maximum altitude acceleration and surge margin check" for the -6 engines? That was something mandated after overhaul or some engine work. I don't think it was done the way you describe though.

I stand by my idiots comment. We lost one of our Lear 25B's in 1980 because they disconnected the overspeed warning.

Additionally, once you reach TOC at 100 FPM, the time it takes to accelerate back to cruise speed can be very long, like 10-15 minutes. It takes a long time to get that speed back once you lose it.

if you "overclimb", then you end up slow and your fuel economy would have been better staying lower and going faster.

A key thing is to look at your AOA. If that starts getting over 0.3, it is going to get slow. I like to stay under 0.25 if I can.

Also, if there is any turbulence at all, you don't want to be very high on the edge. A good downdraft could mean you can't maintain altitude, and it means you will slow down at the very least.

Mike C.

Wasn't there a crash a few years back of a jet that a crew were taking on a repositioning flight?

iirc they were light, no passengers so wondered how high they could go. Engines flamed out, couldn't get them restarted.

You'd think wit those big engines, it would shoot right up there.

But, no, it doesn't. FL430 at max gross ISA is the best the original 750 can do, above that needs a step climb. The X+ version can go to FL470 at ISA.

If you want to go to FL510, older model, max weight, ISA, it takes 434 minutes (over 7 hours), 3405 nm of distance, and 12,744 lbs of fuel. I surmise people don't go up there very often.

Just goes to show you that up there, the air is very thin and no engine is truly big enough.

I routinely fly at FL400/410 and it seems enticing to fly higher to get out of some headwinds. But now I realize I'm not doing that much worse than some much larger airplanes.

Mike C.

I did a bunch of “accel checks” on the 20 series Lears and CF-700 powered Falcons. Always a fun time when they compressor stalled and quit. Most of the time the igniters kept them running after the pop if you were quick to pull the thrust lever back when it stalled, but not always.

My favorite was when both engines needed to be checked. Sometimes the non-test engine decided it wasn’t happy and would stall on you while checking the other.

Are the engines appreciably spooling down at all during the accel checks? Wondering if there was a bump in cabin altitude

Many moons ago I was SIC in a Lear25D on a flight from Athens, GA to Oklahoma City with 4 very unfrequent flyer pax. PIC was a longtime Lear pilot and always wanted to save as much fuel as possible. We were fat, dumb and happy at FL430, but he just had to go to 450 to get a bit more mileage. We hadn't been at 450 for one minute when I heard the biggest bang I've ever heard in a plane and all the engine gauges on the left engine rolled back to zero. Big time compressor stall. The pax weren't happy. We were able to relight the engine at 24,000' and diverted to Memphis, A mechanic looked in the front and back of engine and didn't see anything, so we went on to OKC and then back to Athens at FL270. Pulled the engine after that, and it's quite amazing it still ran. Those GE CJ610s were tough. Flying the 20 series was definitely fun.

So a compressor stall actually damages the engine on a turbojet?

Thanks for the back up, I think it’s pretty obvious now that part of buying a Lear 20 series was to take it up and make sure both engines are good. I talked to a Lear expert today for a refresher, it has to do with the moving stator, and how you handle the throttle.

I’m not inclined to say more because there’s no benefit, because no one flies them anymore and I’ll just have someone picking at everything I say.

Translation: I don't know what I'm talking about and am unable to go into any level of depth about what I post on this topic

So a compressor stall actually damages the engine on a turbojet?

Translation: I don't know what I'm talking about and am unable to go into any level of depth about what I post on this topic

The compressor stall discussions reminds me of an episode when we were preparing for a USAF proposal on the TTTS program. We proposed a 500 series Citation derivative.

The proposal manager said that if there was a compressor stall during the stall portion of the flight evaluation, we would lose.

We came up with a compressor bleed valve whose opening was triggered by the AOA system. It reduced the compressor stalls to a few muffled pops as thrust was increased during stall recovery.

During the USAF flight evaluation, ours had the few muffled pops, the Beechjet banged away, and the Learjet had a flameout.

The proposal manager was right; we lost.