The name sounds familiar. I was at D10 from 2000-2023 on the control room floor the whole time. I knew faces and talked to all of them from time to time, but there were only a few I got to know more than just their initials.

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.

Mike - I’m not sure where you are getting your numbers, but I can say they aren’t accurate.

I have been to 510 in a 2000 model X a handful of times and it didn’t take near that long.

One time leaving the service center in Wichita in a straight X on a test flight full of fuel with crew, two engineers and test equipment in the back. The route was ICT over New Orleans, over key west, over jax, to pxv, back to ict. We were at 510 for 75% of a 5ish hour flight.

Being up to about 470 was ok, 490 was squishy, 510 was like balancing on the head of a pin.

Brad

They came from the Cessna manual.

To FL510, ISA, max weight, 434 minutes, 3405 nm, 12,744 lbs, 102 FPM climb at the end.

From the OM for SN 0001 to 0172. I don't think the numbers change much for the next SN range.


Did you start at max weight? Was it ISA?

Mike C.

To which I would add that I wouldn’t consider anything much less than 300fpm an acceptable climb rate with two engines. It’s not a good situation to be out of mojo at TOC. Even if the book says you can do it, doesn’t mean it’s a good idea.

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.

It was years ago, so I have no idea as to ISA, but we would have been really close to gross weight in the examples.

Again, those charts make no sense because the X (I flew SN 127) only held 13000 # of fuel topped.

I see the charts, they don't agree with my real world experience at all but I can't fully explain the why . Part of it can be explained away by the lower left of the chart - the wind effect portion but not enough for the difference I saw actually operating the airplane.

They do look about right for what I saw through 430 or 430, but from there they make no sense. If you are at 430 @ ISA in 22 minutes, and the chart says you are sill climbing at 288 FPM, but then it says going from 430 to 450 take another 54 (81 - 27) minutes via a step climb, something doesn't add up.

I will see if I can find my old books and see if I can find the difference.

Brad

The highest I ever was on a Citatition X was FL470 to witness a hot fuel climb test. We quit there because the fuel was cooling faster than the airplane was climbing, rendering further climb non-critical.

I know the feeling - had the V35B to FL200 once!
Took 30 min and 50nm to get there!

I miss the days when riding high in a 20 series Learjet was a regular occurrence, man they were rockets.

Take them up until you reach dual flame-out… “yep, those engines are strong” always a relief when they started running again, even though from up there we could have dead sticked to another state.

I have a video somewhere, it was one of the last 20’s to head south forever, they took off the day before the noise rules banned all but the few hushed airplanes from the US.

Of all of the aircraft I’ve had the pleasure of being around, the Lears left an indelible mark, especially the 20 series. It was the good ol’ days and I didn’t even know it.

Seriously? I've been around Lears from 1977 until the 20 series went away. Many test flights to altitude. I've never had a crew so irresponsible.

What kind of idiots did you hang out with?

To be clear, you take them up until they start popping, a few seconds of silence and then they start running again.

Two of the most experienced Lear guys in the world.

Doesn’t mean that they aren’t idiots.

But, we prefer “Cowboys”

Good news for you is that they’re both old now so you don’t have to worry about them reading this and showing up on your doorstep.

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.