On at least a dozen recent flights by U.S. jetliners, malfunctioning equipment made it impossible for pilots to know how fast they were flying...

Typical media hype... All they need to do is stick their hand out the window. :-/

Think I'll stay off A330's.

"malfunctioning equipment made it impossible for pilots to know how fast they were flying"

That is a big exaggeration, IMHO. There are back up systems to the point of redundancy in aircraft, especially commercial jets. Maybe the primary air speed indicator failed, but no way was it "impossible for pilots to know how fast they were flying".

P. Bunyan is making a categorical statement that he may have trouble backing up.

True there is redundancy in systems. But it is clear in the trade literature I have seen that the Airbus has been experiencing multiple failures. Fortunately, in most cases the crew responded appropriately and no tragedy ensued. It is appearing more and more likely that in one case the crew erred--or they were unable to correct the problem.

FYI the pilot's union in France was threatening to boycott the A330 unless the pitot systems were changed from the European manufactured ones to American manufactured systems. I don't know that the boycott occurred; I do know that the systems are in the process of changing.

So did we give the contract for the military fuel-tanker planes to Airbus or to the U.S. company? Airbus seems to have had lots of incidents lately.

While you might be technically correct, Oldflyer, you don't really need to know exactly how fast you are flying to be safe. There are multiple back-up systems to protect the aircraft and occupants. If you are really an OLD Oldflyer, you probably did not have the use of an AOA (angle of attack) indicator. In my opinion, much more accurate and useful than an A/S indicator. Just food for thought....

A pitot-static system is fairly simple but prone to failure if ice or debris blocks the pitot or static ports. That's why these systems have a built-in heater, but that doesn't help if the pitot tube is blocked by a bug. Being the pitot-static system is vital to the safe operation of an aircraft I don't understand why they don't incorporate a GPS based backup system.

In a car you can throw a GPS navication device on the dash and it can not only give you your location, but your speed, and the fancier ones also give you your altitude. In fact, every measurement you can get from a pitot-static system can be derived from a GPS system with sufficient accuracy to operate the aircraft safely. The same is true of the INS (inertial navigations systems) many aircraft use for navigation.

So why don't aircraft manufacturers incorporate these other systems as backup for the pitot-static system knowing that a failure of the pitot-static system puts the aircraft at risk? The only thing I can come up with is that manufacturers think the simple pitot-static system is so reliable that there's no benefit of having an independent backup from something as complex as GPS or INS. Maybe they need to rethink that in light or recent failures.

I am no way qualified to even speculate about these things, but I guess I can ask questions. Don't these transoceanic flights fly in a pretty small envelope? By that I mean aren't they high subsonic and close to stall speed at altitude? It seems to me you have to go pretty fast to stay aloft at 40,000 feet.

On at least a dozen recent flights by U.S. jetliners, malfunctioning equipment made it impossible for pilots to know how fast they were flying...

Just going with the flow of traffic always works for me. :)

That is a big exaggeration, IMHO. There are back up systems to the point of redundancy in aircraft, especially commercial jets.

All jet aircraft have GPS equipment...a Garmin can display ground and IAS. There's your backup.

I am no way qualified to even speculate about these things, but I guess I can ask questions. Don't these transoceanic flights fly in a pretty small envelope? By that I mean aren't they high subsonic and close to stall speed at altitude? It seems to me you have to go pretty fast to stay aloft at 40,000 feet.

No, not really...They do what is called a step-climb. They climb to a certain altitude, burn fuel, getting lighter, step to a new altitude, burn more fuel, etc. They probably fly at their plan flight for maybe 1/3 of their journey, and they DO go pretty fast...around .8-.85 Mach. They actually fly at around 50K feet.

Oh, that was me above by the way....

...I'll also add, that these flights take advantage of the jet stream, and they fly specific altitude/longitude corridors to take advantage of the stream (they are called NAT--North American Tracks, they are standardised tracks, updated daily). There are eastbound tracks (flown during the evening hours) and westbound (flown during the day)

http://en.wikipedia.org/wiki/North_Atlantic_Tracks

A similar set of tracks exist for the Pacific

They actually fly at around 50K feet.

Sorry, I meant the supersonics fly at that altitude. Commercial subsonics travel between 20K-40K

Ugh, sockpuppet begone!

A pitot-static system is fairly simple but prone to failure if ice or debris blocks the pitot or static ports. That's why these systems have a built-in heater, but that doesn't help if the pitot tube is blocked by a bug. Being the pitot-static system is vital to the safe operation of an aircraft I don't understand why they don't incorporate a GPS based backup system.

Pitot ports also provide barometric pressure readings, which are VITAL for ILS and IFR conditions--as they tell you how far above terrain you actually are. GPS can provide this, but not instantaniously, nor as accurately.

Oldflyer, that was my opinion. I am a pilot, but not comercial or anything like that-- just for fun. My cousin does fly 747's, though and I've talked to him alot about it. Anyway there are multiple systems on an Airbus 330.

And Mac, you don't think they have GPS?

And Ricardo: "By that I mean aren't they high subsonic and close to stall speed at altitude? It seems to me you have to go pretty fast to stay aloft at 40,000 feet"

It's the landing and take-off that's the problem.

Here's some very good, fiction but realistic, reading on the subject.

Anyway, I'm not afraid to fly on an Airbus.

#14...
ILS has no input from the pitot-static system...it's strictly electronic.

It's the landing and take-off that's the problem.

Here's some very good, fiction but realistic, reading on the subject.

Never read that book, but based on the wiki, I'm guessing it takes it's events based on the incident with the Russian pilot and his son? (Aeroflot 593)

ILS has no input from the pitot-static system...it's strictly electronic.

No, but the pitot system provides information on altitude and speed, which are needed for keeping on the glideslope.

And if the power goes out, and you are in a dark cockpit with no GPS...

(Sorry, I should have put a comma between ILS and IFR).

I guess what I mean to say is, for level flight, you can get away with a GPS backup, but take-offs and landing are a different matter.

Pitot ports also provide barometric pressure readings, which are VITAL for ILS and IFR conditions--as they tell you how far above terrain you actually are. GPS can provide this, but not instantaniously, nor as accurately.

Actually GPS altitude readings are more accurate then those based on barometric pressure. The weather related component of barometric pressure causes an error of plus or minus 500 feet, which is an order of magnitude larger than the GPS altitude error.

The real issue is in obtaining air speed, which on fly-by-wire aircraft, is used by the various computers to limit or modify pitot input to the flight controls. There are cases where ground crew didn't remove protective tape they put over pitot ports when deicing with the result that the aircraft was nearly unflyable. It such as system it would be nice if the computer could compare pitot, GPS, and INS readings and at least alert the crew to a likely failure and allow the pilot to select one of the backup systems.

While you might be technically correct, Oldflyer, you don't really need to know exactly how fast you are flying to be safe. There are multiple back-up systems to protect the aircraft and occupants. If you are really an OLD Oldflyer, you probably did not have the use of an AOA (angle of attack) indicator. In my opinion, much more accurate and useful than an A/S indicator. Just food for thought....

6. Posted by eblum | August 7, 2009 9:35 PM | Vote up Vote down Report this comment Score: 1 (1 votes cast

The only problem with your theory is that your fancy pants AOA indicator hooks up to that old school pitot-static system. Which is apparently the part that is faulty in the first place.

GPSs et al be damned, flying any aircraft with a faulty pitot tube just ain't safe.

Don't forget about the difference between groundspeed and airspeed. GPS give your speed above ground, so if you're in a 500kts jetstram (tailwind) going 550kts, GPS will return 1050kts while the pitot static system will return the useful 550kts. In the event of a PS failure, groundtrack is useless for flying the plane. It's purely a navigational aid, not to be used for information about the aircraft dynamics.