Back in the news, "Man, we can do it, 41-it," said Cesarz

[Nova]

I answered that question previously, but you seem to be bent on ignoring it. The absolute altitude is irrelevant. When you have 29.92 set on your altimeter, you are reading pressure altitude, and you can enter the table directly. If -44ºC is the standard temperature for 30,000 feet, then it's the standard temperature for FL300. It's just that simple.

It was my error that I stated absolute altitude when I meant to say true altitude. The charts you listed for standard temperatures at altitude are based on True Altitudes while we are flying along at Pressure Altitudes. True and Pressure altitudes will only match when atmospheric pressure and tempreature are standard.

Say you are flying at 17,999' with the current altimeter setting of 29.42 set in the Kollsman window and notice that the OAT is -5 F (standard). That gives you and ISA +0. Now you are cruising at FL180 and tune 29.92 into the Kollsman window. You now find your true altitude to be 17,500' yet you are flying a pressure altitude of 18,000' (high to low look out below). Your OAT will now be reading about -3 F or so. Technically you are still ISA +0 since your OAT is correct for your true altitude. Your method gives you an ISA +2 since you are indicating 18,000 and your standard temperature lists -5 F as the standard temperature.

From what you are saying FL180 = 18,000 feet when it comes to calculating what the standard OAT should be. In nonstandard pressure situations that isn't the case and the charts you list don't account for that. In the flight levels you are flying a isobaric surface not a fixed true altitude. Unless you know the outside air pressure how will you calculate your true altitude? Like temperature, pressure doesn't necessarily maintain a standard laps rate but the rule of thumb may get you close. Plugging in the local altimeter setting from the airport 7 miles below you probably isn't very accurate.

Now the same could be said for temperature variations but the same quote applies, high to low look out below. Here's a refresher:

http://virtualskies.arc.nasa.gov/weather/tutorial/tutorial2d.html

So on a cold, low pressure day you are actually flying quite a bit lower true altitude with the same indicated. I know a few pilots at work who are baffled by the early appearance of the Mmo red line at 10,000' on those days. Given a nonstandard pressure at altitude and large ISA deviation you may have trouble climbing those last few thousand feet to cruise but I guess reading your OAT tells you all of that.

 

[FN FAL]

Hey Tony?

A co-worker was telling me tonight that at his old place of employment, some guys took a Citation III well past it's certified altitude. Obviously, I don't condone such activity, but the story was relayed to me this evening as we were discussing this crash.

If I remember correctly, your PDF on "Core Lock" stated that they test the CRJ from 31,000 feet? Why the lower altitude? Why not 41,000?

Are engines from other manufacturers tested for this "core lock" as well? Is there any chance a turboprop engine could suffer from core lock, or are we operating at altitudes too "warm" for this to happen?

 

[TDTURBO]

I think I learned more from this thread then any other. I don't fly jets either but find both sides of the argument intriguing. I can easily see Novas point and Tony's point making it a bit confusing. I haven't referenced the ISA links because I would probably forget it before I ever fly a jet but I still find both sides credible in the physical sense, especially the 17,999 to FL 180 change in relative density. Just setting your altimeter to 29.92 because you are a foot higher when it was theoretically say 27.72 at 12 inches lower would change things quite a bit I think. Keep this debate up, I want to understand this better.

Tony has done an excellent job of making his point but Nova threw a wrench in it, just for fun, try to explain why this wouldn't make a difference again. Going from the above example.

 

[ultrarunner]

Hey Tony?

A co-worker was telling me tonight that at his old place of employment, some guys took a Citation III well past it's certified altitude.

If I recall, CE-650's are cerficaticated to 510.

How high did your friend say the bozos's took it???


Sounds like a crock of $hit story to me.

 

[TurboS7]

The airplane did fine at 410, the fight crew did everything wrong. Once you get above 370 it becomes a diffrent world. The IAS got to well below 190kts, most airplanes start falling out of the sky at 210kts @410. The got the shaker then the engines flammed out because of lack of air and compressor stalled, bad news. At 410 the averge airspeed should be between 230 and 240 indicated giving around .78 to .80 depending on temp. When you hit turbulence you need to increase mach not decrease it at altitude, you have to say away from the low speed buffet. Once you get to that point there is no turning back. If you do flame out don't even try a start until you get below 250, just be patient, you really have all the time in the world. I know I have had multiple flameouts on test flights, it is no big deal.You just have to relax, these guys did not do that, they were caught with their pants down.

 

[FN FAL]

If I recall, CE-650's are cerficaticated to 510.

How high did your friend say the bozos's took it???


Sounds like a crock of $hit story to me.

Hmmmm...that's funny, because he said 50,000 (or so) feet. I'll have to get back to him on this story again, maybe he thought they were in violation of the aircraft certification, when maybe they weren't.

 

[FN FAL]

If you do flame out don't even try a start until you get below 250, just be patient, you really have all the time in the world. I know I have had multiple flameouts on test flights, it is no big deal.You just have to relax, these guys did not do that, they were caught with their pants down.

Can you ask for block altitudes at that high up? Seems to me, they could have saved themselves a lot of trouble and got the chance to fly 410, if they had left themselves an immediate way out, which wouldn't have required waiting for a clearance or busting one.

 

[TurboS7]

Remember the certified ceiling is based on how fast you can get from altitude to I believe 14000 feet, not on performance. Most light jets can fly well beyound their certified altitude.

 

[aeronautic1]

Lear 31A

We took a Lear 31A to FL510 with no problem.

 

[GravityHater]

you have to say away from the low speed buffet. Once you get to that point there is no turning back.

Does this line mean 'there is no recovery from a full stall, that's it folks'?
Or am I misreading your intention?

 

[TurboS7]

Forget a clearance you just declare an emergency and start on down. In the case of test flights you are in an area that provides that if you need it so usually you don't have to declare an emergency you just tell them where you need to go. I guess you could call that a block altitude of sorts. When the military operates in a restricted area they usually have full block altutide clearance. If the guys in this accident had just pushed over to 240 kts .78 and kept that down to 250 they would have been fine for a relight. After they were established on the decent they could have declared an emergency combined with vectors to a airport. From 410 the airplane will glide 100 to 120 miles, that comes out to almost 20 minutes to get the airplane on the ground. RELAX and think.

 

[TurboS7]

At high altitude in most transport category aircraft, once you are in a full stall you enter a flat spin or inverted flat spin of which there is no recovery. This is typical of all swept wing aircraft. If it happened to me I sure the heck would keep trying, dropping gear changing configurations doing everything to get the CG forward, you never give up. But the design people don't leave a lot of hope, that is why is to so important to do things right. 410 is a very safe place to be, we are there all the time in our 737-800, but you must really treat that part of the atmoshpere with a lot of respect.

 

[TurboS7]

I have had a LR-25D to 510 no problem, we just couldn't get there till we had less than 2000 lbs of fuel. We had the 8A engines and the full pressure masks.

 

[FN FAL]

Forget a clearance you just declare an emergency and start on down.

So, if you go up to 410 in a CRJ and you can't hold alititude at your assigned flight level, you'll just declare your emergency and descend into me instead of thinking ahead and reserving the block beneath you in the event you can't keep the plane up there?

 

[PCL_128]

So, if you go up to 410 in a CRJ and you can't hold alititude at your assigned flight level, you'll just declare your emergency and descend into me instead of thinking ahead and reserving the block beneath you in the event you can't keep the plane up there?

If it's really that questionable that you'll make it up there then you shouldn't be going that high anyway. If I need to request a block of altitude "just in case I can't make it" then I just ain't going that high.