Service Ceiling for New Cessna Jets
 

Cessna has introduced a slew of new airframes , Hemisphere, Longitude, Latitude etc. All have a service ceiling of FL450. The Citation X as well as Learjet, Bombardier jets, Gulfstreams are still capable of FL510.

So why has Cessna limited the new airframes to FL450.

Are flight levels above 450 so seldom used even in 510 capable models that the cost of certification above 450 not worth it.

So a question for the bizjet drivers in FL510 capable airframes, how often do you actually cruise above FL450? It's rare to see anything on flight radar24 above FL450 except for Citation X's and G650's. i do notice that FL410,420,430 are getting increasingly crowded over Europe & North Atlantic. Is there a benefit traffic-wise to going above FL450?

In the X, you had to take 470 minimum to make us of maximum range 430 just wouldn't be enough.

Also keep in mind everything above 410 isn't RVSM. There are no levels 420, 440. Cruising in 410, in need of a higher level, you have to take 450. If 430 isn't enough, 470 is the next higher.

Safelife (glows in the dark)

The main reason I can think of a 450 ceiling vs 510 is cost: a 450 ceiling is cheaper to produce and to sell (engines, wing, etc..).

I fly a 510 capable airplane, and I seldom reach 470, as it is only typically needed for operations close to max endurance with optimum levels to be flown. Most of my flying is between 400 and 450.

I only flew twice at 490, after cabin work and to check serviceability at different levels.

Don't forget the affects of cosmic radiation at the higher levels, another reason many operators don't go there.

Certification during emergency descent is a limiting factor, even with ADM. In Europe RAD is often preventing very high cruising level ( agreement between ATC centers).
At these very high levels, residual thrust is very low, hence you need to be light, since you are looking for the minimum time between two points, you surf the winds. And except for a smoother ride,(or Very long range ops) very high cruising level may not be the best.
Long Range, mean Low and Slow initially, so you might see a plane in the low 40 initially that would climb to 470/490 at the end of the cruise.
For FAA, you have O2 considerations as well..

But as far as the airframes are concerned, the main trigger is really , like said above, cost of certification and manufacturing, the delta P for a 4000 ft cabin at FL510....hmmm pressure cooker..

Cosmic radiation detectors are only required above FL510

Isn't there also the issue of needing a carefully-managed let-down profile to accommodate the conflicting requirements of reducing power sufficiently to descend at an acceptable speed but with enough LP pressure to maintain the cabin pressure?

PDR

In the G650ER at max TO weight (103,600 lbs) initial cruise alt is FL410/FL430 depending on direction of flight. Seeing we don't always need 7,500nm range, with typical 5-7 hour fuel load we normally cruise FL450/FL470... For better rides we find ourselves at FL490 from time to time. Not really an issue for the plane. FL510 is elusive though, you have to be light and ISA has to be good.

The plane flys great at FL470 at .88 and a cabin alt of 4,200ft ish.

j

I was asked to make a 6,000’ crossing restriction once in a Global from F450 or F470. I told BOS ARTCC that I would have be assured of no level on the way down. Idle, M.85/320 and with MAX boards we were over 10,000 fpm down. Cabin never budged up from 4,500’, but the cabin descent rate was pretty good! Lot air has to be pumped in for F510 cert.

gf

I agree with CL300... "Certification during emergency descent is a limiting factor, even with ADM".

That's why the Challenger 601/604/605 and 650 are restricted to FL410.

We fly our Globals between FL410 and FL470 all the time (FL430 and FL450 being the most often used)... On flights from Europe to Montreal we will start at FL430 climb to FL450 at 30W (if ATC allows it) and climb to FL470 prior to coast in with Gander on our way to CYUL... A few times at FL490 but that was on a very long flight like Beijing to Montreal.

20 + years ago, I flew the fantastic Citation 3.

It was certified to FL510, but we never got it above 470. It has the ADM