airmale
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What Happens If An Aircraft Over Flies 40,000?

Wed Jun 04, 2003 4:40 am

I think thats the ceiling, so what could happen if they exceed that height?
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donder10
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RE: What Happens If An Aircraft Over Flies 40,000?

Wed Jun 04, 2003 4:42 am

A lot of the modern ones have ceilings of around 42,000ft.I have Ryanair flights at 40,000feet before!Some 747SPs have been upto 45,000ft!
 
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groobster
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RE: What Happens If An Aircraft Over Flies 40,000?

Wed Jun 04, 2003 4:43 am

Whilst on a flight on New Years Eve from MEL to SYD on an A332 we had to rise to 41000ft to avoid heavy turbulence.

Can't say anything stranged happen to us!
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airmale
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RE: What Happens If An Aircraft Over Flies 40,000?

Wed Jun 04, 2003 4:44 am

And if they exceed 45,000 or more?
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zrs70
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RE: What Happens If An Aircraft Over Flies 40,000?

Wed Jun 04, 2003 4:47 am

The air is too thin to support most aircraft at high altitudes. The plane would need increased speed. Fly too high, and the craft would most likely stall.
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777236ER
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RE: What Happens If An Aircraft Over Flies 40,000?

Wed Jun 04, 2003 4:48 am

Cabin pressure is often the altitude-limiter, not airplane performance.
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tjwgrr
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RE: What Happens If An Aircraft Over Flies 40,000?

Wed Jun 04, 2003 5:54 am

737NG's and 757's routinely cruise up to FL 410, 767's up to FL 430.
Direct KNOBS, maintain 2700' until established on the localizer, cleared ILS runway 26 left approach.
 
Mark_D.
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RE: What Happens If An Aircraft Over Flies 40,000?

Wed Jun 04, 2003 6:05 am

Note that --depending upon whom you ask and what variant it is and payload it's carrying-- the fairly-standard-subsonic-wing-design B-52 bombers have advertised service ceilings of as much as 56 000 ft.


I think this is an interesting article, about airliners' environmental control systems:

http://www.boeing.com/commercial/cabinair/ecs.pdf


Figure 10 near the end shows "cabin altitude" getting rather rarified, when aircraft altitude gets above 40 000ft.

[Edited 2003-06-03 23:08:42]
 
Bellerophon
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RE: What Happens If An Aircraft Over Flies 40,000?

Wed Jun 04, 2003 6:43 am

Airmale

The maximum altitude a civil airliner is certificated to fly at is determined during flight testing, and is imposed because the aircraft has come up against any one of a number of different limitations, depending on the design of the aircraft, its wing, its engines or its cabin environmental systems.

Just to give a few examples:

  • The aircraft engines may not be producing sufficient thrust to enable it to climb any higher.


  • The aircraft wings may not be capable of providing adequate lift at a higher altitude.


  • The Mach Number might become too high, causing undesirable aerodynamic effects.


  • The maximum and minimum speeds may be too close together at a higher altitude


  • If the Cabin pressure were to fail at high altitude, there may not be adequate Oxygen pressure available in the emergency drop down masks.


  • B777236ER raised an important and increasingly common limit, that of cabin air pressure. The air pressure in the passenger cabin must not be allowed to fall below a minimum value, equivalent to a maximum Cabin altitude of 8,000 ft (I think), under both JAA & FAA regulations

    If the cabin altitude is already at the maximum permitted, and the aircraft then climbs, the differential pressure (the difference between the pressure inside the cabin and the air outside the aircraft) will rise as the outside air pressure decreases.

    When you reach the maximum differential pressure, typically around 8 to 9 psi, you cannot climb any higher without breaking one of those two limits.

    I hope these give you some idea of the varied reasons that can determine how high an airliner is allowed to fly, and why it is not a good idea to exceed the limit. There is even one airliner where the maximum altitude can be limited by the temperature of the nose!

    Provided that the aircraft is certificated to fly above 40,000 ft - and many now are, with one being cleared to fly at 60,000 ft - it will be perfectly safe up there, and nothing untoward will happen.

    However, deliberately flying any aircraft above its maximum certificated altitude, unless you are a qualified test pilot on a well planned test flight, is one of the dumbest things you can do whilst airborne.

    Regards

    Bellerophon
     
    Yikes!
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Wed Jun 04, 2003 7:50 am

    A B52 is not going to fly at 56,000'.

    It's not possible.

    As altitude increases, indicated airspeed decreases.

    As altitude increases, temperature decreases to a standard -56 degrees C.

    It is not uncommon to see -65 degrees C or colder in a non-standard atmosphere.

    Consequently, to maintain an indicated airpspeed at higher altitudes, true airspeed (or equivalent Mach number) must increase. If it doesn't, the IAS decreases to the point the aircraft stalls. The B52 is a 1950's technology airframe. It is not capable of high Mach capability. Even with ISA -20, the Mach number required to maintain an IAS > Vs will exceed the B52's Mcrit.

    Especially given the ancient technology of their 8 pure turbojets. The engines might be willing (flat out) but the airframe is wanting...

    Original Question: The B767 is certified to fly at FL420. Concorde is certified to (I think) FL 650. Rembember though that Concorde cruise climbs at M2.0

     
    redngold
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Wed Jun 04, 2003 8:21 am

    But... 45,000 ft. is approaching that coffin corner for a lot of aircraft. They MUST slow down or change AOA to remain stable in flight. Otherwise you get an incident like that Northwest Airlines 727 that took a dive out of the sky over Michigan.

    redngold
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    Mr.BA
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Wed Jun 04, 2003 8:30 am

    It's because the higher you go, the speed margin is minimal. You must be very careful to ensure airspeed does not drop too much or you might not have enough thrust to increase the speed back cruising speed for example. And the higher one goes, the KIAS drops, so it's closer to stalling.
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    Mark_D.
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Wed Jun 04, 2003 8:46 am

    Well sites like this claim 55 000 ft (sorry, I guess I had remembered incorrectly with the 56 000 number)

    http://www.aerospaceweb.org/aircraft/bomber/b52/index.shtml

    But then writers like this guy mention 50 000 (and says they never went that high anyway)

    http://www.jimclonts.com/bio.htm


    Airframe supposedly able to handle Mach .91

     
    hmmmm...
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Wed Jun 04, 2003 8:50 am

    At more rarefied altitudes, an airliner is in an environment that is very unforgiving of a sudden change in AOA. The aircraft could lose stability and control very easily and go into a nose dive. It's happened. The higher you go the less air to ride on, the easier it is to lose control and the harder it is to recover immediately.

    If you have MS Flight simulator, program your aircraft for a very rarefied altitude and watch what happens when it loads. The plane will tumble and drop like a rock and you will not be able to recover until you get down to lower altitudes. I once did this with the soar plane, I loaded it in at 80,000 ft, and the bloodly thing tumbled wildly until I got down to 45,000 ft. simply because there was not enough air to ride on. If you were to magically insert an airliner at, say, 80,000 ft, it would plummet like a rock. The dynamic forces would probably destroy it before it could recover at a lower altitude.
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    brons2
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Wed Jun 04, 2003 8:56 am

    Coffin corner is the reason, you get to a point at higher altitudes that the margin between a stall (as IAS decreases) and overspeed (mach too high) becomes very, very small.
    Firings, if well done, are good for employee morale.
     
    Yikes!
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Wed Jun 04, 2003 9:04 am

    AIRLINERS CAN'T EXCEED MACH 1.0

    (Except for Concorde)

    Mach 1.0 is a Brick Wall. In fact, it is less than 1.0, usually in the range of .90

    Given that fact; given that the B52 airframe is a < M1.0 airframe ; given the old generation engines (engine inlet ducting needs to be specialized to exceed M1.0 too), yadda yadda...

    You might want to take this over to the Tech forum...
     
    AA717driver
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Wed Jun 04, 2003 12:23 pm

    I've seen aircraft at 450. I've been to 410 a few times in the 757. The 767 will do 430 but it has to be really light. I think the GIV's and GV's can do 510.

    It's not like Icarus, you know... Big grin TC
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    IMissPiedmont
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Wed Jun 04, 2003 1:11 pm

    But Yikes!, Mach is mach period, never 0.90 mach or 1.07 mach.

    And there are indeed several biz jets certified to fly in the low 50s.
    The day you stop learning is the day you should die.
     
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    derekf
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Wed Jun 04, 2003 8:39 pm

    Yikes!
    You are wrong. A DC-8 exceeded Mach 1 in a dive during a test flight. There are also rumours about the VC-10.
    Mach 1 is not a barrier - thats what everyone thought in the 1940s. BTW I've been to 45000ft in a 125 where we had only 210kts and 0.8M.

    D
    Whatever.......
     
    Mr.BA
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Wed Jun 04, 2003 8:46 pm

    And does anyone recall the China Airlines B747SP which survived the dived through Mach1.0?
    Boeing747 万岁!
     
    Guest

    RE: What Happens If An Aircraft Over Flies 40,000?

    Wed Jun 04, 2003 9:14 pm

    Surprised to see this question here - why not Tech-Ops...?
    xxx
    The "ceiling" (maximum operating altitude-level) is a certification number...
    For transport airplanes (airlines) it is generally an altitude limit for pressurization, that is, maintaining at least 8,000 feet (2,500 meters) equivalent pressure in the cabin...
    xxx
    Many transport airplanes are certificated to 35,000 feet (old 737s)
    Other older airplanes (707, 727, DC8) are certificated to 42,000 feet...
    The 747 is certificated to 45,100 feet...
    Some Learjet types are certificated to 51,000 feet...
    The Concorde is certificated to 60,000 feet...
    xxx
    For all above airplanes, this is the level at which their cabin will reach 8,000 feet OR limited by the time it would take them to reach 14,000 feet in case of an emergency descent for failure of the pressurization system...
    xxx
    The 747 I fly is legally limited to 45,100 feet, yet, when I was in the Air Force, the E-4 (747 Command Post) was able, in emergency (and when very light in weight) to reach nearly 48,000 to 52,000 feet... at the verge of a stall...
    xxx
    When airplanes are heavy (fuel for very long trip) they are far from able to reach high levels... With my 747, we can barely reach 29,000 feet when we are fully loaded for a trip from Argentina to Europe, yet, at the end of the cruise flights, we occasionally are at 39,000 feet... I hardly ever fly at the maximum certificated of 45,000 feet...
    xxx
    Such a question really belongs to Tech.Ops -  Big grin
    Happy contrails...
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    727LOVER
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Wed Jun 04, 2003 9:15 pm

    Red N' Gold,

    I believe it was TWA.....N840TW to be exact.
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    FutureFO
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Wed Jun 04, 2003 10:26 pm

    I had been on a CO flite to EWR from LAX and we were at FL415 on a 757-200.
    I Don't know where I am anymore
     
    jmhLUV2fly
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Wed Jun 04, 2003 10:39 pm

    From what a AirTran 717 first officer said to me once, my understanding is that for the 717 at least the max altitude that airplane can really go is 35.0 any higher then that and from what he said the wings really are not designed to support the aircraft much above that altitude...
    now most definitly for your 747's and 777's , A340s etc
    they are designed to fly really high 40.0 or so altitude if need be... for max fuel burn etc, I mean keck the trips they commonly serve are 12+ hour flights so it would make sence for them....but not all airplanes can fly that high.
    JMH
     
    deltairlines
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Wed Jun 04, 2003 10:40 pm

    I've climbed regularly to FL410 on 747, 757, 767, and 777 before.

    I don't think I've gone higher than that on a conventional airliner (read: not Concorde)

    Jeff
     
    ZSSNC
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Wed Jun 04, 2003 11:30 pm

    Yikes!,

    above 36000 feet temperature actually increases up to about 150000 feet where it starts to decrease again.

    ZSSNC
    Airbus A340-600 - the longest temptation in the sky
     
    Yikes!
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Wed Jun 04, 2003 11:57 pm

    No, above the tropopause, in a standard atmosphere, temperature remains constant with increase in altitude. When reaching the stratopause, you are then correct. If my met recall is correct.
     
    Yikes!
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    RE: Derekf

    Thu Jun 05, 2003 12:02 am

    "Yikes!
    You are wrong. A DC-8 exceeded Mach 1 in a dive during a test flight. There are also rumours about the VC-10.
    Mach 1 is not a barrier - thats what everyone thought in the 1940s. BTW I've been to 45000ft in a 125 where we had only 210kts and 0.8M.

    D"

    I of course was referring to maximum normal operating speed. Many airliners have accidentally entered the regime in excess of their Mcrit and have paid a price for it in structural damage or failure. Perhaps I should have worded my statement "designed" to exceed Mach 1.0

    Take a look at a drag curve from an aerodynamics text as local speed of sound is approached.

    As far as taking your bizjet to the limit of its altitude, you better hope you have extremely smooth air!
     
    kevi747
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Thu Jun 05, 2003 12:10 am

    I believe I've been to 45,000 ft in a 767. Is that possible? One time I was hanging out in the cockpit flying from JFK-LAX. I noticed that we had recieved a message over the ACARS printer that read: Can you see the curvature of the Earth from up there?

    When I brought it to the Captains attention she just laughed. I looked at the altimeter and it said (or this is how I remember it anyway): 45,000.

    Does anybody know if that's possible?

    "Reality has a well-known liberal bias." --Stephen Colbert
     
    Yikes!
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    RE: IMissPiedmont

    Thu Jun 05, 2003 12:11 am

    "But Yikes!, Mach is mach period, never 0.90 mach or 1.07 mach.

    And there are indeed several biz jets certified to fly in the low 50s."

    Don't understand your first statement - please clarify.

    Second: of course. They've been designed to cruise at higher altitudes with improved powerplants and supercritical wings. The Cit X can cruise at M0.92.

    Now compare the sleek, modern, aerodynamic area-ruled design of the C-X with a B52 designed in the 50's. Saying nothing of engine efficiencies...
     
    FDXmech
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Thu Jun 05, 2003 12:15 am

    >>>Mach 1.0 is a Brick Wall. In fact, it is less than 1.0, usually in the range of .90<<<

    Interestingly, the slow A310 with its thick wing and supercritical airfoil, at cruise speed, has supersonic airflow flowing over most of its wing.

    You're only as good as your last departure.
     
    FutureFO
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Thu Jun 05, 2003 2:26 am

    The 727 has demonstrated cruise speeds of .91-.95M but be it as a short burst of speed and at a higher altitude to get the performance.
    I Don't know where I am anymore
     
    Rick767
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Thu Jun 05, 2003 3:09 am

    Kevi747

    "I believe I've been to 45,000 ft in a 767. Is that possible?"

    Not legally / safely. See below for the max alts.

    "When airplanes are heavy (fuel for very long trip) they are far from able to reach high levels... With my 747, we can barely reach 29,000 feet when we are fully loaded for a trip from Argentina to Europe, yet, at the end of the cruise flights, we occasionally are at 39,000 feet... I hardly ever fly at the maximum certificated of 45,000 feet..."

    B747skipper sums this topic up nicely. On the 757-200 we can go to 42,000ft (in practice FL410) and on the 767-300 we can go to 43,100ft (in practice FL430).

    I have never seen these levels in passenger service on either aircraft. We fly our 757s with 235 passengers and our 767-300s with 315-328 passengers. Our flights are nearly always full.

    On transatlantic trips with the B763 FL290 - FL320 is about the highest we can go initially, with the optimum level hanging around the FL305 mark. Getting a NAT track at FL320 is about right as the optimum level will be rising as our gross weight reduces along the track and we can "bracket" the optimum level. Remember that at the other end the optimum will likely be above us in the FL345 mark off the top of my head.

    Then we can step to FL350 and stay there for the rest of the trip. FL390 sometimes, FL410 only if weather dictates as this is never optimum in our operations due to high ZFW.

    On the 757-200 we can usually go straight to FL360/FL370 for a European hop (2-4 hours). Stepping to FL380/FL390 is not really ever worth it unless weather dictates, as the optimum weights to climb to these levels are in the 80,000kg range and often that is less than our ZFW!

    Short, empty positioning flights are the exception to these rules - we can go
    pretty much straight to FL410 in both aircraft in these cases.

    Brons2

    "Coffin corner is the reason, you get to a point at higher altitudes that the margin between a stall (as IAS decreases) and overspeed (mach too high) becomes very, very small."

    Close but not close enough!! The margin actually becomes zero, so the speed at which high speed buffet and low speed stall occurs becomes the same.

    THAT is "Coffin Corner".

    It is the reason attempting to out-climb thunderstorm cells is normally a futile exercise since these things can grow to over 60,000ft and you'd hit Coffin Corner long before that.

    For interest you can find the optimum / maximum weights for various cruise levels for the B757 at:

    http://www.757.org.uk/limits/lim8.html

    and for the 767...

    http://www.757.org.uk/767/limits/lim8.html
    I used to love the smell of Jet-A in the morning...
     
    IMissPiedmont
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Thu Jun 05, 2003 11:47 am

    Mach 1.0 is a Brick Wall. In fact, it is less than 1.0, usually in the range of .90.

    I guess I misread what you meant by this Yikes!. I must learn to read the previous post better. In my haste I interpreted the sentence to read that Mach could be .90 when you meant the coffin corner, didn't you?

    I guess my assumption was a bit silly.
    The day you stop learning is the day you should die.
     
    LSTC
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Fri Jun 06, 2003 10:45 am

    What happens when an airplane goes above 40,000 feet? Everyone gets real high!

     Smile

    The 42,000+ foot service ceiling you often see has much to do with certification of the airframe.

    There are "special conditions" that must be met at these extreme altitudes because of the inherent danger of hull breeches at these altitudes and because of the lack of certification standards contained in FAR 25 for these instances. Take a look at the Type Certificate for any of these high flying machines, and you'll see a "special condition for high altitude" as part of the certification basis.

    Depressurization at intermediate altitudes (up to 35,000 feet) is not a catastrphic event, since demand oxygen masks supplied in the cabin and the cockpit are capable of delivering oxygen to humans at that altitude.

    Above that altitude, there is a chance that due to the lack of required differential pressure, the human lung cannot utilize the oxygen drawn in by breathing. Oxygen must be forced into the lungs by pressure. There are several internet sites that discuss this phenomenon so I won't go into the details here.

    Although its commonplace to have these "pressure" masks in military airplanes, commercial airline cockpits have "demand" type masks that have a semi-pressure function that only slightly pressurizes the oxygen delivered.

    Anyway, if an airplane is certifed to altitudes above 35,000 feet, the airframe must be designed to much more critical standards to prevent the catastrophic event of a depressurization. The airplane must also demonstrate that the cabin will remain pressurized during the worst case established during certification. One business jet I have been involved with needed to maintain pressure with a 9 inch hole in the fuselage at 52,000 feet.

    One interesting thing is that civil airworthiness authorities have different philosophies of how to develop these special conditions of airworthiness. Thats why the FAA Type Certificate defines the service ceiling of the 757 as 42,000 feet and the TCCA (Canada) Type Certificate states 41,000 feet.

    [Edited 2003-06-06 03:45:58]
     
    flightsimfreak
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Fri Jun 06, 2003 3:44 pm

    I have been to FL 390 in a NW 757 from MSP to PDX...

    I have proof too.
     
    L-188
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Fri Jun 06, 2003 4:31 pm

    Yeah Mr.Ba I do remember that aircraft, Can't recall if it was a China Air plane or not but it seems right.

    I belive that it was only shown mathmatically that it was possible for the aircraft to have exceeded M1 in that dive but it isn't recorded officially. They did manage to rip the doors off the LG bays during recovery.

    I want to say that you can get some of the later gulfstreams up to Fl540 but don't hold me to that. For commercial aircraft there is very little advantage for going that high.
    OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
     
    Bellerophon
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Fri Jun 06, 2003 7:45 pm

    LSTC

    Good post, but just one tiny quibble:

    ...commercial airline cockpits have "demand" type masks...

    Most do, certainly, but not quite all!  Big grin

    Flight crew pressure breathing masks are fitted on my aircraft type, and we are examined yearly in their correct use, under the supervision of a specialist av-med doctor.

    Regards

    Bellerophon
     
    LSTC
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Sat Jun 07, 2003 3:00 am

    Bellerophon,

    That's interesting. Was it a regional requirement to have pressure masks? Could you tell me what kind of things they look for on your anual check? Also, is it a difficult thing to get used to? Or is it well within the average person's capability?

    Thanks!
     
    777kicksass
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Sat Jun 07, 2003 6:26 am

    Bare in mind that Concorde operated safely at altitudes at up to 64,000feet (i think- correct me if i'm wrong)!!

    The only health risk is that if you were to fly very regularly at that altitude you get adverse effects from high amounts of UV rays. I suppose these could include skin cancer and eye problems, but thats hardly ever going to happen.
     
    ben
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Sat Jun 07, 2003 8:11 am

    UV rays

    I doubt UV is much of a problem... dont you mean cosmic radiation?
     
    citationjet
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Sun Jun 08, 2003 1:17 pm

    The Citation X (Model 750) has a maximum operating altitude of 51,000 ft. Also in flight flutter testing to Md of Mach 0.99, they exceeded Mach 1.0 slightly. A T-38 was being used as chase aircraft.
    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.
     
    Bellerophon
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    RE: What Happens If An Aircraft Over Flies 40,000?

    Mon Jun 09, 2003 1:03 am

    LSTC

    It is a UK/French airworthiness certification requirement for the aircraft that pressure breathing apparatus be available for the flight crew. The airline's Air Operators Certificate requires that the crew be trained and regularly examined in its use.

    Not too difficult to use, but quite different from a conventional flight crew demand oxygen mask, and requires good initial instruction and some practice to use correctly.

    A few crew don't like the sensation, but all manage to use it effectively and pass the tests.

    Following the appropriate training, it should be well within the capabilities of all pilots to use.

    During each yearly check, the correct donning and use of the mask is observed by specialist av-med doctors. The main points they watch for are:

  • Mask correctly deployed within a very short time limit.

  • Mask fitted tightly to the face (otherwise the air flow will just lift the mask off you face, rather than forcing air down your lungs).

  • An ability to talk effectively (you have to exhale very hard, against the pressurised in-rush of air, to generate any sound from your larynx).

  • Normal breathing rate, no hyperventilation, no hypoxia.

  • An ability to perform normal tasks and mental calculations correctly.



  • 777kicksass

    Maximum authorised altitude for Concorde is 60,000 ft.

    UV radiation is not a factor.

    Cosmic radiation has the potential to be, and so is checked pre-flight with a radiation forecast, and monitored whilst airborne with on-board equipment. In practice, it is never a problem.


    Regards

    Bellerophon

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