Air France crash? 2

[Higgler]

Now that pitot tube icing has been confirmed, were the pilots pulling up to slow their speed?

Why don't pilots carry an aircraft capable GPS with them in the cockpit to see their ground speed? I say aircraft capable because one pilot I knew bought a $120 GPS that had a software load which would not display speeds above 100 mph, just to make you buy the much more expensive $400 aircraft GPS.

 

[rb1957]

static ports read static pressure, pitot tube reads total pressure, the difference gives you dynamic pressure and hence airspeed. (no?)

if the static ports are stuck at SL, your computer is going to have trouble understanding a -ve dynamic pressure.

 

[IRstuff]

True enough, which is why there are radar altimeters, and have been for, what, 50 yrs? Interestingly, there was an anecdote that in Vietnam, the F-111 terrain following mode had faulty radar altimeters, which would be switched out in favor of the barometric altimeters. The instaneous change in apparent ground distance would hiccough the flight computer and caused several crashes.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[thruthefence]

rb1957 is correct, it reads the delta, in airspeed.

example, if I hook up my Barfield pitot/static tester to an aircraft's airdats system (and for the sake of this example, lets not have an air data computer in the mix), and I apply NEGATIVE pressure ie, below field elevation, to the STATIC port, the apparent airspeed of the indicator will increase.

Conversely, if (after returning the system to field elevation) I close off the static port reference, and attempt to add pitot pressure, it would require a much higher pitot pressure to achieve n airspeed (on the indicator), then if the static port is open to ambient pressure.

 

[Zoomeri]

GPS/INS Enhancements to FMSs

After shaking my head on what's coming out of the CVRs and the black boxes, I'll go out on a limb and make a prediction on how the flight management computers will be upgraded to help prevent future occurrences.

1) enable the flight control system to record GPS and INS vertical/horizontal data;
2) by comparison of GPS and INS speed data to the aircraft's ADC, the FMS can calculate *and store* the corresponding winds aloft components;
3) should a failure occur in the ADC, the FMS could then step down to output speeds provided by both GPS and INS, adjusted by the stored wind data in order to display semi-accurate computed horizontal/vertical airspeeds. I believe the computed airspeeds would accurate enough to fly the plane safely.

Obviously the accuracy of the stored winds aloft data would degrade as the aircraft moved to a different geographic zone, but that occurs over many minutes during which the crew would be able to sort themselves out to prevent the type of situation that befell AF447.

Does anyone know if this has already been tried out?

 

[rb1957]

maybe i'm wrong (again) but isn't INS speed the same as GPS speed (ie ground speeds).

maybe they should get a bigger dog ... the joke being the plane's computers fly the plane quite well enough, and they put a dog on the flight deck to prevent the pilot's from touching anything.

 

[dik]

Is there not some type of pressure indicator that could be kept ice free that would have a correlation with air speed?

Dik

 

[KENAT]

Sort of, the one that some other airlines had already installed on their Airbus A330s.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[IRstuff]

Sure, isn't that called a heated pitot tube?

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[IRstuff]

And, yes, inertial correlates to GPS, more than anything else.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[moon161]

Airspeed is not exactly the velocity relative to the local atmosphere. The pitot static system gives you dynamic pressure and the lift and control effects that follow. The airspeed is how fast you would be moving relative to sea level standard air. At constant velocity, this decreases with altitude. So at high altitude, your stall speed bumps up against your max speed.

Ref. Coffin Corner

http://en.wikipedia.org/wiki/Coffin_corner_(aviation)

 

[rb1957]

that depends on which airspeed you're using ... true (the local airspeed), equivalent (local airspeed adjusted for sea level conditions), indicated (equivalent adjusted for instrumentation errors), calibrated ...

 

[dik]

I wasn't thinking of a heated pitot tube. There are pressure sensors available, that are completely closed units (I doubt they would work if iced over, but don't know) They are solid state and not of the pitot tube variety.

I think there is a distinct correlation between pressure and speed. Several could be combined to determine overall flying condition.

They are also light weight and relatively inexpensive for the ones I've seen literature on.

Dik

 

[IRstuff]

" distinct correlation between pressure and speed"

There's a distinct correlation between pressure DROP and speed. That's the whole point of a Pitot tube.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[rb1957]

insert "dynamic" before pressure ...

dynamic pressure = 1/2*rho*V^2

IKYK

 

[debodine]

Here is an link to an article by a person who claims to be a very experienced A330 pilot. His information blows my theory completely out of of the water due to the lack of sidestick feedback to the pilot and the bit about the throttles not moving with thrust changes under autothrottles. How anyone could set Attitude + Power = Performance and thereby avoid entering a stalled condition with that design philosophy is beyond me to understand.

I highly recommend reading this article becasue if he truly is an A330 pilot, his perspective is far more valuable than mine.

http://www.avweb.com/eletter/archives/avflash/1925-full.html#204756

 

[dik]

Thanks, IR and rb1957... but, I knew about Mr. Bernoulli... I would still suggest that there was 'a distinct correlation', even if it's inversely proportional to the velocity squared.

Dik

 

[IRstuff]

I think that you'll find that the aerodynamic drag equation is nontrivial to undo in real life. The effective drag area proportionality "constant" isn't constant. Additionally, the stagnation pressure is also affected by the static pressure, rain, ice, etc. You'd still need a pitot tube to measure the static pressure.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[berkshire]

IR stuff
Ok what am I missing here? I thought a pitot tube measured dynamic pressure. I thought a static port measured static pressure.
The fact that the two are frequently incorporated into one sensor head, I though was co incidental.
B.E.


The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[rb1957]

i thought this headline in AW&ST was relevant, given the posts about using "non-traditional" instruments (ie GPS) ...

"tests confirm GPS jamming by LightSquared" ...
"Initial testing of GPS receivers confirms aircraft navigation systems will experience significant jamming from thousands of broadband-wireless transmitters planned to be deployed across the U.S."

 

[berkshire]

rb1957
Are you talking about this?
The AOPA is already popping and spitting about it.
B.E.

LIGHT ADVISORY LightSquare Testing May 16, 2011 – May 27, 2011 Boulder City, NV
Notice Number: NOTC2978


FLIGHT ADVISORY

LightSquared Testing at BVU


May 16, 2011 – May 27, 2011 Boulder City, NV
LightSquare (mobile broadband service) testing is scheduled as follows and may result in unreliable or unavailable GPS signal.

More information can be downloaded from the link below.

https://www.faasafety.gov/files/notices/2011/May/Light_Square_-BVU_Flight_Advisory.pdf

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor