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Air France jet missing over the Atlantic

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Member
Registered: May 2009
Posts: 125
Quote
From memory, air data systems can provide 4 measurements of use to the pilot, barometric altitude, air speed, stall warning and angle of attack.


... vertical speed, total air temperature, static air temperature, mach, TAS, impact pressure for engine fuel control, etc....

AOA vanes are used on all Boeings and the 737NG even has an optional AOA indication on the primary flight display. AOA vanes are the primary reference for computing stall speeds on the 744.

Quote
A few types of aircraft, use different forms of static sources and air data ports, such as carefully placed holes in the aircraft skin.


I guess you could say Boeings also have different forms of static sources. Some are located on the pitot probes, others are on the fuselage.

Cheers.
Q>
Member
Registered: May 2009
Posts: 269
Location: between EDDF and EDDN
Qavion wrote
I'm sure I can think of some much worse case scenarios... e.g. localised windshear, wind gusts of a hundred knots or more, etc, not experienced by aircraft flying along the same route a few minutes earlier (and I doubt that there would be aircraft flying all routes every few minutes).
+/-20kts could stall or overspeed the aircraft, especially at high altitudes.


Hi Qavion,

worst case scenario in this case was meant as no reliable airspeed indication due to loss of all pitot tubes. If you have gusts of 100 kts and more in FL 390 you will be in trouble if your pitot tubes are working or not.

For the GPS or INS backup: I think it should be possible to say that in a certain altitude with ISA conditions at a certain N1 a rather exact IAS, Mach, TAS and GS (with zero wind) is achieved. For the 747 e.g. cruise tables are in the manual in which you can see what IAS, MACH and TAS, N1 and FF parameters you have in a specified FL and grossweight range.

These figures of course differ due to weather conditions. A change of temperature will change IAS / Mach relation (and as I understand your comments also N1 and FF) and a change of wind changes TAS / GS relation.

Reversely it should be possible to calculate wind components from the existing parameters, at least for a short period of time which should be sufficient to descent to a safer more uncritical FL (perhaps the altitude in which an aircraft must descent in case of loss of cabin pressure)

The GPS knows the actual GS and TRK and FL. I'm not sure if the GPS also knows the HDG. But the INS/IRS should know. These data compared with the "should have" GS and HDG from the last known conditions gives you the wind component.

It is clear that this will not be an exact calculation. It only can be an approximate calculation. And its also not meant to conduct an entire flight this way. These thougts just came up to minimize the chance of accidents as we probably had on AF 447.

Peter
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Registered: May 2009
Posts: 5140
Hi Dominic.

Dominic Manzer wrote
The Blue Angels once crashed four or five planes at once because they violated their air-show barometric altitude procedure. The acrobatic procedures are written in altitude above ground level (AGL) so the procedure dose not need to be rewritten (and relearned) for each airport. But this requires that the altimeter be set to sea level before takeoff.

I assume this is a typo and should read "airport elevation" instead of "sea level"?

Regards,

|-|ardy


Edit: Any my typo is: It shouldn't read airport elevation, but airport pressure. Pascal, not feet.
« Last edit by Hardy Heinlin on Wed, 10 Jun 2009 05:57:18 +0000. »
Member
Registered: Jun 2009
Posts: 20
Hardy Heinlin wrote
Hi Dominic.

Dominic Manzer wrote
The Blue Angels once crashed four or five planes at once because they violated their air-show barometric altitude procedure. The acrobatic procedures are written in altitude above ground level (AGL) so the procedure dose not need to be rewritten (and relearned) for each airport. But this requires that the altimeter be set to sea level before takeoff.

I assume this is a typo and should read "airport elevation" instead of "sea level"?

Regards,

|-|ardy

You made my point, by crashing. You made the same mistake they did! If you need say 1400 ft to complete a maneuver and start the maneuver when your altimeter says 1500 ASL, as the Blue Angles did, you will be OK as long as the ground elevation is less than 100 ft. If the ground elevation is 1000 ft, you started the maneuver at 500 ft AGL, have 900 ft too little altitude and are in big trouble.

Knowing how things work and why is essential when something unusual happens or is done. In the Blue Angels' case they memorized the procedure altitudes in AGL. The procedure is written in AGL so they hit the same altitude marks every-time, but the altimeter must be set to read AGL. Flying the routine in above Sea Level measurement at a new ground level airport every week is impossible, as the crash showed.
Moderator
Registered: May 2009
Posts: 5140
I guess we're having a lingual rather than a technical misunderstanding here.

I'm saying:

If I want my baro altimeter to agree with the AGL-altitude printed on the chart (while flying at that AGL-altitude), I have to set my baro not to sea level (QNH), but so that it reads zero when I'm parking at the airport (QFE).

When I would be overflying La Paz at 1000 feet AGL and my baro would be set to sea level (QNH), my altimeter would read something around 14000! Not 1000.

And when I would land in La Paz with QNH set instead of QFE, my altimeter would read ca. 13000, not 0.

Don't say you disagree :-)

|-|ardy


That lingual misunderstanding may lie in in the word "this":
Quote
The acrobatic procedures are written in altitude above ground level (AGL) so the procedure dose not need to be rewritten (and relearned) for each airport. But this requires that the altimeter be set to sea level before takeoff.

What is the word "this" refering to? To procedures written in AGL? Or to procedures rewritten in QNH?
« Last edit by Hardy Heinlin on Wed, 10 Jun 2009 01:42:00 +0000. »
Member
Registered: May 2009
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Location: Chicago
(USA knowledge only here) Do any other countries require that pilots set QFE? It would make no sense for the USA (or Bolivia) to require QFE, since we have airports that are many thousands of feet in the air. But not every land is so topographically diverse. So do any use QFE?

Will
« Last edit by Will on Wed, 10 Jun 2009 02:32:54 +0000. »
Member
Registered: Jun 2009
Posts: 20
I should have said "elevation set to Zero on the runway." After sending my first reply I realized that "set to sea level" could be interpreted several ways and I was unaware of the meaning pilots attach to the phrase. Set to airport elevation and set for airport elevation also have dangerously overlapping meanings. I bring this up just to highlight how difficult it can be to write procedures that cannot be misinterpreted.

Review and debate is at the hart of any scientific investigation, including crash investigation. I have not seen the actual Blue Angels air-show procedure so I don't know if there was ambiguity in the procedure or if the pilots simply missed or forgot the deviation from standard take off practice. This brings up another good point, the procedures that are used daily by many people quickly get scrubbed of any problems. But procedures that are infrequently used, and then only in the invariant environment of a simulator, do not (and can not) get the kind of every day testing necessary to resolve all potential problems. A subtle change in context can cause a different interpretation to emerge that will have disastrous consequences.
Moderator
Registered: May 2009
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Will, as far as I recall, Russian charts sometimes refered to QFE. Don't know how it is today.

Dominic, so you use the term "sea level" as a synonym for "zero feet"?

|-|

I'm just realizing that we both fooled each other. Actually, airport elevation is QNH, and sea level is QNH as well. Either refers to ... well, QNH. What we both meant while typing is: QFE. Set the baro so that the altimeter reads zero when we're on the ground.
« Last edit by Hardy Heinlin on Wed, 10 Jun 2009 02:57:10 +0000. »
Member
Registered: Jun 2009
Posts: 20

What is the word "this" referring to? To procedures written in AGL? Or to procedures rewritten in QNH?

This referred to the Blue Angles air show procedure being written in AGL.
Member
Registered: Jun 2009
Posts: 20
Hardy Heinlin wrote
Will, as far as I recall, Russian charts sometimes refered to QFE. Don't know how it is today.

Dominic, so you use the term "sea level" as a synonym for "zero feet"?

|-|

I'm just realizing that we both fooled each other. Actually, airport elevation is QNH, and sea level is QNH as well. Either refers to ... well, QNH. What we both meant while typing is: QFE. Set the baro so that the altimeter reads zero when we're on the ground.


QED


QED is from latin meaning, It is proven. :)

I would say I used it as a synonym, this may be the first time I've ever used the phase "set to sea level." I don't have any particular meaning permanent attached to it.

P.S. My spell checker has problems with each of our spelling of "referred." I too like the looks of "refered" but at close inspection it has to be "referred."
Moderator
Registered: May 2009
Posts: 5140
Another potential lingual problem is the missing unit when talking about an altimeter setting: Is it about an altitude value or about a pressure value?

In other words, when we say "set baro to airport elevation" we should also say if we're meaning the altitude of the airport above sea level (QNH) – or the pressure at the airport (QFE). When we set airport pressure in La Paz we need to rotate that little baro knob a zillion times.

|-|
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Posts: 2449
Location: KTMB
QFE: last World Flight we had lots of it, it is quite common when operating in meters, though obviously unrelated technically.

You do get caught if you don't expect it. Especially if in the middle of the (real) night while having had too little sleep and already overstressed listening to busy ATC in half Russian to other planes. The big trick is that the altimeter setting isn't obviously totally different and you don't need to press any special button. If you are in your normal routine during approach and have pre-set the altimeter according to international weather reports, there is a good chance you miss the exact numbers from ATC but do pick up the altitude, now AGL.

We knew the QFE trick but when we got there, it was good we were on manual and we could cross-reference to typical pattern radio height habits... :roll:

I recall that it was exactly the controller's insistence on QFE, repeat QFE, that made me doubt. Suddenly I thought this was something so different that I had to DO something, but I forgot what. The answer is: NOTHING, of course. Just set the altimeter as told... don't think.
« Last edit by Jeroen Hoppenbrouwers on Wed, 10 Jun 2009 04:23:04 +0000. »
Member
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Posts: 125
I guess someone, somewhere, uses QFE....

User posted image
Member
Registered: May 2009
Posts: 125
Don't forget that when you set your baro to QFE using the EFIS control panel, this also affects the pressurisation system. The selection (option) on the APPROACH REF page, I am told, will ensure the pressurisation system operates normally in QFE mode (just don't ask me how! :P )
Member
Registered: May 2009
Posts: 202
Location: Sydney, Australia
Qavion wrote
Don't forget that when you set your baro to QFE using the EFIS control panel, this also affects the pressurisation system. The selection (option) on the APPROACH REF page, I am told, will ensure the pressurisation system operates normally in QFE mode (just don't ask me how! :P )

How? :mrgreen:
_______________
Member
Registered: May 2009
Posts: 269
Location: between EDDF and EDDN
Will Cronenwett wrote
(USA knowledge only here) Do any other countries require that pilots set QFE? It would make no sense for the USA (or Bolivia) to require QFE, since we have airports that are many thousands of feet in the air. But not every land is so topographically diverse. So do any use QFE?

Will


Hi Will,

In Germany gliders pilots use QFE and metric units. Even on the same airfields where all other aircrafts fly with QNH.

http://www.moeve-obernau.de/Habicht_Cockpit_600.jpg

Don't ask me for the reasons and if this is required. It is just like it is. 8)

Peter
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Location: KTMB
More news, in German:
http://www.stern.de/reise/fernreisen/:Vor-Brasilien-Lufthansa-Jumbo-Turbulenzen/703165.html

Two days before the AF crash, in the same area, a Lufthansa 747-400 hit very heavy turbulence without any warning.
Member
Registered: May 2009
Posts: 958
Location: Chicago
Hardy, can you implement the QFE option like Q showed in his post above? I think it's basically a requirement that you add this. (How else could you land properly when gliding into a grass field in Germany?) Also... can any 747 reset the altimeter to meters? Seems like an easy option for Boeing to implement.

Will
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I sometimes humorously advise people who are afraid of turbulence during a normal flight that the aircraft can withstand perhaps + or - 1G loads without much risk (from distant memory I think an airliner can do maybe 1-2 G but I can't recall - it's not an aerobatic aircraft), plus a safety factor. Thus, if the stewardess is floating in mid-air, there is a negative 1G stress on the aircraft, nothing to be worried about. If she has been forcefully slammed into the ceiling and is stuck there by the forces or if she is walking upside down on the ceiling, it is probably time to get a bit nervous. I always keep my seat belt fastened - too many stories about severe clear air turbulence are told.

I think it was supposedly Galileo who said that in the absence of air resistance, a feather would fall just as fast as a cannon ball in the earth's gravitational field. Perhaps one could use such physics to better understand the effects of severe turbulence on physical objects.

If the most recent turbulence-caused acceleration of the aircraft in a vertical direction is so severe that things fly up towards the ceiling for a moment, it would be a concern for passenger comfort at least. I don't think it would risk the airframe unless it were severe and/or prolonged. Yet a **sustained** 1G or greater vertical acceleration would surely pose problems of many types if it continues for very long (grins).

I've always thought with some anxiety while flying as a passenger in an airliner that at 600 miles per hour (=10 miles per minute), and since it is only about 5-7 miles to the ground, it would only take about 30 seconds to impact the earth if somehow the airliner began flying straight down. Perhaps it would never reach the ground since it would presumably go supersonic before diving too far. (more grins)
_______________
Best wishes,

Phil Bunch
Member
Registered: May 2009
Posts: 414
Location: Mumbai, India
Phil Bunch wrote
... things fly up towards the ceiling for a moment ..


I think this is what Hardy was talking about; things are not moving (initially), the aircraft is moving around them.

Hardy, I guess this is a natural human way of describing things from our perspective. Just as we speak about 'sunrise' and 'sunset', whereas the sun is doing no such thing.

Shiv
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Registered: May 2009
Posts: 5140
Shiv Mathur wrote
Hardy, I guess this is a natural human way of describing things from our perspective. Just as we speak about 'sunrise' and 'sunset', whereas the sun is doing no such thing.

Sure, but the Stern magazine usually claims to provide professional journalism. Instead, the author just copied the words of a witness without checking the content. The entire article is rather an exaggeration, not only regarding the meal carts. Well, the main thing is, their web site gets lots of hits.

|-|ardy
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P.S.: The joke doesn't lie in the fact that the earth moves during sunset, or that the aircraft moves instead of the meal cart. The joke is that the author uses the heavy weight of the cart to demonstrate how strong the turbulences were. He makes the reader to believe, that heavy objects follow the aircraft better than light objects do (in reality, it's vice versa). He sells this observation as an exciting sensation.
Member
Registered: May 2009
Posts: 269
Location: between EDDF and EDDN
Hardy Heinlin wrote
Sure, but the Stern magazine usually claims to provide professional journalism. Instead, the author just copied the words of a witness without checking the content. The entire article is rather an exaggeration, not only regarding the meal carts. Well, the main thing is, their web site gets lots of hits.


What is professional journalism?

All newspapers and magazines, especially those with white letters or signs on red ground claim this. But the facts are: there must be a headline, which make the reader look at it. And there must be an captivating article behind. If this article is correct or not is secondary.
In my experience there is no big difference between the popular press and the so called quality papers.

In the company I work for, we made the experience - except for specialized technical press, for which we write the articles by ourselves and they print it as they are - that the journalists write what they want. Even if we give them a clear manuscript and also have personal interviews the the article is published in a different way.

Once we claimed, that the content of the printed article not only was distorted, it was definitely wrong. We were told, that this is not wrong. It just is journalistic freedom...

This is no joke. And unfortunately this is quite usual.

I think is is better to have this in mind, when reading newspaers or magazines.

Peter

PS: I'm not only a fan of flying meal carts but especially of flying roast chickens :mrgreen:
Member
Registered: May 2009
Posts: 146
Hey Hardy, recently hoppie posted a video of a Pogo Stick in the Galley of the PMDG 747 can we expect and Elephant on a Desk when we leave the PSX Flightdeck :):):)

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