SNBru
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Altitude Of 39000 Ft

Fri Sep 30, 2005 7:09 pm

My last SN flight was a BRU-TLV flight with an A319. The onboard route information screen informed us that we were flying at 39.000 ft. This is the highest altitude I ever noticed on a flight I guess.

My question: what is the maximum altitude for normal operated commercial flights and isn't an altitude of 39.000 very high compared to the average 33.000 ft?
How is the optimal altitude defined?

Thanks
 
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ZSOFN
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RE: Altitude Of 39000 Ft

Fri Sep 30, 2005 8:56 pm

39K is actually quite normal. EZY routinely fly their 73Gs (not been on their A319s yet) at 38/39k. Older a/c like F100s, DC9s etc may fly at closer to FL310/330 etc but it's quite normal for A32Xs/73Gs to fly higher.
 
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TripleDelta
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RE: Altitude Of 39000 Ft

Fri Sep 30, 2005 10:20 pm

Even during warm weather, when aircraft performance is generally reduced due to the lower air density, some airliners fly high, even on relatively short hops. ZAG - CDG is about 1h 50 mins and the OU A319 I was going with to CDG for the Paris Air Show topped out at FL380. Coming back to ZAG, a completely full A320 got up to FL390.
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Jetlagged
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RE: Altitude Of 39000 Ft

Fri Sep 30, 2005 10:33 pm

Nothing to do with the age of the aircraft. I once flew in an ancient B720 at FL390. Fokker 100s and DC-9s are capable of operating at FL390 too. Most twin jets will have the excess thrust to climb to high levels quickly, while four engined "heavies" on long flights are initially weight limited, so might start cruising at FL310, then step climb to FL350 or higher as the fuel burns off.
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SlamClick
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RE: Altitude Of 39000 Ft

Fri Sep 30, 2005 10:49 pm

Quoting Jetlagged (Reply 3):
and DC-9s are capable of operating at FL390 too.

The "ten series" was only certificated up to 350.

It is not just a performance issue. It is pressure differential, and time required to get back down below a certain altitude in the event of loss of cabin pressure.

Where performance is a factor is well illustrated by the B-727-200. The 200s with dash-seven engines don't have the oomph to push you up very high. Those with dash fifteen or dash seventeen engines will happily drive you right on up to where the wings won't support it anymore. The flight speed envelope gets quite narrow up at very high altitudes for many older planes. Even the 737-700 has enough thrust to get you up where the high speed and low speed limits are only a few knots apart.
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Starlionblue
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RE: Altitude Of 39000 Ft

Sat Oct 01, 2005 12:34 am

Quoting SlamClick (Reply 4):
The flight speed envelope gets quite narrow up at very high altitudes for many older planes. Even the 737-700 has enough thrust to get you up where the high speed and low speed limits are only a few knots apart.

The well known "coffin corner". For the TR-2 (formerly known as U-2) it's only 10 knots from overspeed to stall speed, and the plane has no autothrottle. Whoooo...
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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Jetlagged
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RE: Altitude Of 39000 Ft

Sat Oct 01, 2005 2:26 am

Quoting SlamClick (Reply 4):
The flight speed envelope gets quite narrow up at very high altitudes for many older planes.

Not just an older aircraft "feature". Supercritical wings can be just as badly affected.

Quoting Starlionblue (Reply 5):
The well known "coffin corner". For the TR-2 (formerly known as U-2) it's only 10 knots from overspeed to stall speed, and the plane has no autothrottle. Whoooo...

I think you mean the TR-1. As I understand it, "coffin corner" is where the mach buffet and stall buffet speeds coincide. At that point you have nowhere to go. In contrast, the 0.3g buffet limits of an airliner are the manoeuvring limits. Exceeding them does not mean you will fall out of the sky, unless you are turning significantly at the time. 0.3g equates to about a 40 degree banked turn.
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SlamClick
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RE: Altitude Of 39000 Ft

Sat Oct 01, 2005 4:33 am

Quoting Jetlagged (Reply 6):
Not just an older aircraft "feature". Supercritical wings can be just as badly affected.

Absolutely correct. I sort of alluded to that with:

Quoting SlamClick (Reply 4):
Even the 737-700 has enough thrust to get you up where the high speed and low speed limits are only a few knots apart.

. . . but I must confess I don't know what the differences are between 737NG wings and those of the classics, apart from the greater span and area.

Quoting Jetlagged (Reply 6):
In contrast, the 0.3g buffet limits of an airliner are the manoeuvring limits.

Can I assume you mean 1.3G for maneuvering? Actually it was also quite common to flight plan at 1.5 or 1.6G when turbulence is forecast at cruise altitude.
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SlamClick
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RE: Altitude Of 39000 Ft

Sat Oct 01, 2005 4:43 am

Quoting Starlionblue (Reply 5):
For the TR-2 (formerly known as U-2) it's only 10 knots from overspeed to stall speed, and the plane has no autothrottle. Whoooo...

One of my former students was a U-2 Instructor Pilot. I guess what you said is very true, but he said that most people who do not pass the checkout fail it on visual approaches. Apparently they use a shallow approach with the engine almost unspooled and it is rather demanding.

Here's one I used to share with my students, dispatchers and pilots alike.
From a performance manual for B-737-300 with CFM-56-3-B1 engines:
With 1.5G buffet boudary protection.
Flight Level 330
120,000 lbs cruise gross weight
The low speed limit is 254 Knots and the high speed limit is 260 Knots.

That is a four-knot window! Wouldn't take much in the way of a shear to depart that envelope, one way or the other.

If you level off at the same weight at FL310 the envelope expands to 240/283. I consider that a real good option. If you stay at 310 until you burn off another five thousand pounds of fuel then climb to 330 you now have 240/268. For those of us who are ham-fisted pilots that seems like a good deal.
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mrocktor
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RE: Altitude Of 39000 Ft

Sat Oct 01, 2005 5:53 am

To answer the otehr part of the question, the maximum practical altitude for commercial aircraft is 41,000ft.

Two issues drive that limitation: the time of useful consciousness at that altitude is less than 15 seconds. This means the pilots have 15 seconds to recover from surprise, identify decompression and put on their masks. Flying higher would further reduce this margin to the point of unfeasibility.

The second issue is that almost all conventional aircraft have engines whose plane of rotation intercepts the pressurized section of the fuselage. This means that an uncontained rotor failure can puncture the pressure vessel. The accepted model for a large rotor fragment is one third of the disk (a 120 degree pizza slice).

The FAR Part 25 requirement for pressurization states that cabin altitude may not exceed 40,000 feet (exceeding must be considered catastrophic). You can imagine how fast decompression occurs with a hole that size. If you are flying above 41,000 feet, you cant get below FL400 before pressure equalizes.

These factors mean that certifying a commercial jet for flight above 41,000 feet is not practical. Business jets get around this problem by placing the engines aft of the pressure bulkhead. Since rotor failure cannot rip open the fuselage, the largest hole they have to contend with is some antenna breaking off. This means that depressurization will be a lot slower allowing time for descent below FL400. Some of these jets do use overpressure (open air conditioning inflow to the maximum and close outflow) to further reduce the depressurization rate.

mrocktor
 
Whiskeyflyer
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RE: Altitude Of 39000 Ft

Sat Oct 01, 2005 11:16 pm

some older jets are restricted to lower altitudes due to (1) fatigue limits. We have a complete set of structural inspections to carry out because we fly above FL300, primarily lap joints requiring NDT. (2) RVSM its not worth the money or hassle getting RVSM approval so now we flying low in the FL200s, burning more fuel.
Mrocktor........ some nice comments you made. I learnt something new today and I thought the rear engines where there so the crew could sleep in a nice quiet cockpit
 
bhill
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RE: Altitude Of 39000 Ft

Sun Oct 02, 2005 12:37 am

Slamclick, sir, by "shear" do you mean where the two boundries of the jet streams meet and a wind velocity differential exsists?

Regards
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SlamClick
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RE: Altitude Of 39000 Ft

Sun Oct 02, 2005 1:39 am

Quoting Bhill (Reply 11):
do you mean where the two boundries of the jet streams meet and a wind velocity differential exsists?

Well yes, and more. I was referring to any of the conditions that can cause an abrupt change in the wind direction and speed, horizontally and especially vertically.

This would include, for example, the polar side of the jetstream core as well as mountain wave. Then sometimes there are just atmospheric anomalies like the "Lakeview bump" a small area of light turbulence that many of us have experienced in the mid-thirties in the vicinity of the LKV VOR. It is probably a remnant of the wave from the Cascade mountain range but it seems to exist even on days with relatively light winds aloft.

I have experienced a severe loss of airspeed downwind of the Cascades. I don't know how bad it would have become or how long it would have lasted but we got "any altitude between 280 and 350" from ATC, punched off the autopilot and started a descent - chasing airspeed. In a few seconds we flew out of whatever it was and were able to climb back to 350 and resume normal cruise.

It is likely that passengers never noticed anything but a bump or two, but I would not have wanted to be in the coffin corner when he hit that.
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bri2k1
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RE: Altitude Of 39000 Ft

Sun Oct 02, 2005 1:40 am

I believe shear refers to any boundary between differently moving air masses, horizontal or vertical. The jet stream could certainly produce a shear plane. Even a light breeze aloft could generate the 2-3 knot differential needed to stall or overspeed that plane at that altitude though.

What happens then? I know an overspeed can result in structural damage and even engine failure depending on design. What about going too slowly? If I stall a plane and don't make an immediate, positive recovery, I'm going to lose altitude. So, if the U2 stalles at FL330 and loses some altitude, is it going to be in denser air, with a lower stall speed, effectively breaking its own stall?
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SlamClick
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RE: Altitude Of 39000 Ft

Sun Oct 02, 2005 2:28 am

Quoting Bri2k1 (Reply 13):
So, if the U2 stalles at FL330

I believe that the U-2 had its more serious problems up at higher altitudes, perhaps around 70000 feet. At FL330 it should have an envelope much like any other plane. Guesses there, as I'm not remotely qualified to talk about the U-2.

Quoting Bri2k1 (Reply 13):
If I stall a plane and don't make an immediate, positive recovery, I'm going to lose altitude. So, if the U2 stalles at FL330 and loses some altitude, is it going to be in denser air, with a lower stall speed, effectively breaking its own stall?

Remember that even though you are going too slow to fly, at high altitude you still have a high mach number, a mach number possibly in the trans-sonic range (0.75 to 1.2 Mach) The dynamic airloads are still extremely high on the airplane's surfaces. The U-2 was a rather fragile airframe. So if you depart stable flight at some unimaginable altitude there is still enough airload to break the wings off it.

Second problem is that of compressor stalling. At that kind of altitude abrupt throttle movements might well cause uncontrollable compressor stalls and guess what - you are headed for lower altitude for a restart, no matter where you are in the geopolitical world.

The public was told during the Frank Powers affair that he'd had a flameout and had to descend to a lower altitude, where the missile got him. In his book he said that he was hit at his overflight altitude which was higher (around a hundred thousand, I gather) than the Air Force would even admit the plane could do.

As for finding denser air on your descent; again I'd guess that you would have to descend a very long time before the air thickened up enough to be of any real use to you. Remember you got there by using your engine (in the middle of its envelope) to push your wings up the middle of their envelope to an altitude where they could no longer support flight if anything upset them. Then something did upset them. Recoveries are much more difficult outside the envelope.
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Starlionblue
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RE: Altitude Of 39000 Ft

Sun Oct 02, 2005 3:02 am

Quoting Jetlagged (Reply 6):
Quoting Starlionblue (Reply 5):
The well known "coffin corner". For the TR-2 (formerly known as U-2) it's only 10 knots from overspeed to stall speed, and the plane has no autothrottle. Whoooo...

I think you mean the TR-1.

Mu apologies. It is indeed the TR-1.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
timz
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RE: Altitude Of 39000 Ft

Sun Oct 02, 2005 6:30 am

"These factors mean that certifying a commercial jet for flight above 41,000 feet is not practical."

But you're not saying none are certified above FL410?

I thought I once heard a 747SP at FL430-- think I'm remembering wrong?
 
iRISH251
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RE: Altitude Of 39000 Ft

Sun Oct 02, 2005 8:05 am

I heard an Air France 747-400 on a DUB-CDG ferry flight climbing to FL450 and reporting level! Also, when Aer Lingus had 767s, I once heard one en route LHR-DUB (about a 50 minute flight) at FL430 - both very unusual occurrences, I think, but presumably fully legal.
 
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Jetlagged
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RE: Altitude Of 39000 Ft

Sun Oct 02, 2005 9:29 am

Quoting SlamClick (Reply 7):
Can I assume you mean 1.3G for maneuvering? Actually it was also quite common to flight plan at 1.5 or 1.6G when turbulence is forecast at cruise altitude.

Yes, the manuals I've seen and the data I've used refers to them as 0.3g buffet margins, which equates to manoeuvring flight at 1.3g. Margins may vary from aircraft to aircraft, on the 737-3/4/500 the buffet margin displayed on EFIS and annunciated on the FMC is 0.3g.
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bhill
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RE: Altitude Of 39000 Ft

Sun Oct 02, 2005 10:27 am

SlamClick, sir, I believe I know what you might be referring to. SEA is my "homeport" and I remember on initial descent on a NWA DC-10 a few years back experiancing a rather "uncomfortable" roll to the starboard and a single sudden drop of altitude, and my body being forced forward against my seatbelt. As I was sitting in a window seat, there was only the cirrus clouds around as you described earlier. I am still amazed at the suddenness and abruptness that caused that large aircraft to change flight like that. As if a "giant" hand was pushing against and down on the aircraft..mayhaps 2-3 seconds tops.

Regards
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khenleydia
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RE: Altitude Of 39000 Ft

Sun Oct 02, 2005 11:05 pm

Quoting Irish251 (Reply 17):
Also, when Aer Lingus had 767s, I once heard one en route LHR-DUB (about a 50 minute flight) at FL430 - both very unusual occurrences, I think, but presumably fully legal.

There is a picture on a.net of the cockpit of a 767 and the altimeter clearly indicates FL430. From what I have read and been told, they are certified to that level. I also seem to recall hearing that a few other commercial airliners were certified to fly at that level, but don't remember which.

Does anyone know some of the higher altitude certified commercial airliners?

Thanks.

KhenleyDIA
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mrocktor
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RE: Altitude Of 39000 Ft

Mon Oct 03, 2005 12:51 am

Quoting Whiskeyflyer (Reply 10):
I learnt something new today and I thought the rear engines where there so the crew could sleep in a nice quiet cockpit

The rear positioning of the engines has many resons, ground clearance being one of the foremost. Pressurization is one fo the many variables in the decision.

Quoting Bri2k1 (Reply 13):
So, if the U2 stalles at FL330 and loses some altitude, is it going to be in denser air, with a lower stall speed, effectively breaking its own stall?

As SlamClick posted, the hard part is maintaining post-stall control of the aircraft. If you manage to maintain a decent attitude avoiding structural failure, recovery should be possible (in aircraft that don't have deep stall characteristics, at least).

Quoting Timz (Reply 16):
But you're not saying none are certified above FL410?

I thought I once heard a 747SP at FL430-- think I'm remembering wrong?



Quoting Irish251 (Reply 17):
I heard an Air France 747-400 on a DUB-CDG ferry flight climbing to FL450 and reporting level! Also, when Aer Lingus had 767s, I once heard one en route LHR-DUB (about a 50 minute flight) at FL430 - both very unusual occurrences, I think, but presumably fully legal.

I'm sayiing that the certification rules today are like that. At the time the 747 and 767 were certified, the rules may very well have been different. The advisory circular referent to uncontained rotor failures was published in 1989, for instance.

mrocktor
 
citationjet
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RE: Altitude Of 39000 Ft

Wed Oct 05, 2005 11:39 am

The 707 max altitude is 42,000 ft.
The 720 max altitude is 42,000 ft.
The 727 max altitude is 42,000 ft.
The 737-100, -200 max altitude is 35,000 or 37,000 ft.
The 737-300, -400, -500 max altitude is 37,000 ft.
The 737-600, -700, -800, -900 max altitude is 41,000 ft.
The 747 max altitude is 45,100 ft.
The 757 max altitude is 42,000 ft.
The 767 max altitude is 43,100 ft.
The 777 max altitude is 43,100 ft.

The DC-10 max operating altitude is 42,000 ft.
The MD-11 max operating altitude is 43,200 ft.
The L-1011-385-1 max operating altitude is 42,000 ft.
The L-1011-385-3 max operating altitude is 43,000 ft.

Some business jets are certified to higher altitudes.
The Cessna Citation X (Model 750) is certified to 51,000 ft.

Here is a link to the FAA Type Certificate Data Sheet web site that has all the certification information.
http://www.airweb.faa.gov/Regulatory...keModel.nsf/MainFrame?OpenFrameSet

.

[Edited 2005-10-05 04:50:28]
Boeing Flown: 701,702,703;717;720;721,722;731,732,733,734,735,737,738,739;741,742,743,744,747SP;752,753;762,763;772,773.
 
Aviation
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RE: Altitude Of 39000 Ft

Wed Oct 05, 2005 1:47 pm

Id say 39,000ft is high but still in the normal range i have been on many flights were we cruise at 38,000ft never been to 39,000ft but id say its fine a 737 can fly to 44,000ft can it not is this its service ceiling?

Thanks,
Aaron J Nicoli
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mrocktor
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RE: Altitude Of 39000 Ft

Thu Oct 06, 2005 5:08 am

Quoting CitationJet (Reply 22):
The 737-600, -700, -800, -900 max altitude is 41,000 ft



Quoting CitationJet (Reply 22):
The 777 max altitude is 43,100 ft

Great information CitationJet! The 777 is a fairly recent aircraft, but it's certification basis probably precedes 1989. I wonder what the limits are for the more recent Airbuses, they could shed some light on how the rules stand nowdays.

mrocktor
 
Tornado82
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RE: Altitude Of 39000 Ft

Thu Oct 06, 2005 8:42 am

From the meteorological standpoints of this...

Quoting Bri2k1 (Reply 13):


I believe shear refers to any boundary between differently moving air masses, horizontal or vertical.

Yes, in a simplified term.

Quoting Bri2k1 (Reply 13):
The jet stream could certainly produce a shear plane.

Yes, definitely.

Quoting Bri2k1 (Reply 13):
Even a light breeze aloft could generate the 2-3 knot differential needed to stall or overspeed that plane at that altitude though.

Well, it depends which altitude you're talking about. At the U-2 altitudes, which I believe were like FL600 or higher, there would be such little amount of windflow because you're typically well above the tropopause, which is generally speaking the upward boundary of "weather" as we know it here on land and in the flight levels known to any commercial aircraft. If I'm wrong on the U-2 altitudes i'll stand corrected, just let me know, no offense will be taken. If you're talking about the 737 altitudes though... there would be all kinds of air pockets to cause a 2-3kt differential. Such pockets occur even on the surface so of course they'd occur up there.

Another thing to keep in mind is that FL390 is not always correlated with 39,000 feet MSL. Since 39,000 is really just a pressure level once the pilot sets his altimeter to 29.92 (at FL180, right??) the height at which that pressure surface occurs varies greatly. Varying heights of pressure systems are what causes warm and cold. Generally speaking, warm days will create higher heights for a pressure level, cooler days will create lower heights. Also, something such as an "Upper Low" when watching the weather forecasts means that the heights in the atmosphere for say for instance the 500mb level, are significantly closer to the ground than they would be on a "normal" day. Anyone with any further questions about the meteorological aspects feel free to fire away... or send me an IM on here. I tried to stay as brief as possible, sorry though about the length.  Smile
 
bri2k1
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RE: Altitude Of 39000 Ft

Thu Oct 06, 2005 7:55 pm

Very informative thread. Thanks everyone for the good info.
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Allessandro
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RE: Altitude Of 39000 Ft

Fri Oct 14, 2005 1:44 am

There is one thing I miss in all your information... and that is the maximum differential pressure the aircraft can handle... the cabin altitude is most of the time not higher than 8.000 ft, and when the aircraft climbs the differential presure will cause stress on the fuselage. For some aircraft this maximum pressure is the limiting factor. For instance the Fokker 100 and Fokker 70 are limited to FL350 while they are able to climb much higher (I believe FL390 can be reached without to much problems) but because at FL350 and cabin altitude of 8.000 ft the max differential presssure is about 8.45 Psi it is limited to FL350.
 
bri2k1
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RE: Altitude Of 39000 Ft

Fri Oct 14, 2005 2:04 am

I seem to recall flying out of ONT on UA listening to channel 9. We were on LA Center and had just switched to a higher-altitude sector frequency. For spacing, the controller was requesting indicated flight level and mach number from various aircraft. One particular flight, I don't remember the carrier or callsign, reported FL 400 at M 0.82. A curious pilot on another flight asked "What type of plane is that?" And some other pilot responded "A fast one!" I don't remember exactly what the answer was, but it might have been a 747. Good times.
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Luke
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RE: Altitude Of 39000 Ft

Fri Oct 14, 2005 3:09 am

As far as I know, the FMC on most modern aircraft have the function of determining when the aircraft is light enough to step up to a higher flight level. I'd like to know what kind of range between minimum and maximum speeds it requires before it will show the step climb to be 'safe'.
 
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Starlionblue
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RE: Altitude Of 39000 Ft

Fri Oct 14, 2005 3:49 am

Quoting SlamClick (Reply 8):
One of my former students was a U-2 Instructor Pilot. I guess what you said is very true, but he said that most people who do not pass the checkout fail it on visual approaches. Apparently they use a shallow approach with the engine almost unspooled and it is rather demanding.

Yepp. On final another U-2/TR-1 pilot will drive along the runway next to the plane to help guide the pilot in. Considering the low approach speed with those megawings it's quite doable (the driving that is).

[Edited 2005-10-13 20:49:56]
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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TripleDelta
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RE: Altitude Of 39000 Ft

Fri Oct 14, 2005 5:04 am

Quoting Starlionblue (Reply 30):
Yepp. On final another U-2/TR-1 pilot will drive along the runway next to the plane to help guide the pilot in. Considering the low approach speed with those megawings it's quite doable (the driving that is).

Don't they usually drive behind the U-2/TR-1? I have a picture or two of that in a book on "black jets" and it looks pretty intense. Something for the kid in all of us Big grin. The caption by the picture says that the pilot in the car chiefly helps by calling out the aircraft's altitude above the runway.

As far as the book mentions, today they're using '95 5.7L Camaros, replacing the original '87-'91 5.0L Mustangs.
No plane, no gain.
 
cfcuq
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RE: Altitude Of 39000 Ft

Fri Oct 14, 2005 5:16 am

I read once that early in the U-2 program, they used SS 396 El Caminos (68-9) and placed the outrigger landing gear on the wing ends from the Camino while in motion. The Caminos started launching along the runway while the U-2 was several miles out on final.
 
SNBru
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RE: Altitude Of 39000 Ft

Sun Oct 23, 2005 9:17 pm

Thanks for all the information.
 
bond007
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RE: Altitude Of 39000 Ft

Mon Oct 24, 2005 7:50 am

Sorry, got on this thread late.

Looking at some US flight plan data I have the following info:

Many Learjet 45's, Global Express, and Gulfstream 5's cruising at FL490.

The highest airliners I see in the past 6 months over FL410 have been Cargolux B747-400's ate FL450.

Some United B777-200's at FL450, but all on UAL 99nn callsigns, so presumably test flights or deliveries ...not scheduled pax flights.


Jimbo
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