You're quite correct. There are multiple suppliers, however the aircraft manufacturer owns the design. Probe vendors are given the drawings and manufacture to the aircraft manufacturer's design specification.

To complicate matters further, there are in addition, approved repair stations that can "repair" a probe that has been eroded out of specification or where the heater has failed. They don't actually repair the probe at all, they rebuild it to the original drawings but at a lower price than the original probe manufacturer charges for a brand new replacement.

The result is not a PMA part, it comes back with the same Part Number and Serial Number as the probe that was sent for repair. A bit like restoring an old aeroplane using nothing but the original data plate.

may I throw in
 

another question..

we may need a dedicated pitot / air data system specialist to answer that after some soul searching..

am i correct??

heated probes are part of the anti-ice protection of any transport aircraft..

having said that, "anti-icing", like in "heated" are preventive anticipating systems..

(or "have been")

we all know the old probes, that had been heated to the max from take-off to touch down..same heat as in "very hot"..may not have been the most elegant way, they did look "burnt" after awhile, but as long as they worked one could be pretty sure that whatever nature would throw at them, those things kept free of ice..

now, with the newer probes, as I understand, those are controlled by thermostats.. for all kinds of good reasons maybe..

however, as we know, problems with newer type probes always surfaced in a highly dynamic environment, i.e. sudden temp & humidity changes..

could it be that by the philosophy of the newer designs, that their heating circuits by nature simply do not respond fast enough to sudden temp & humidity changes, i.e. perverting the "anti - ice" philosophy to the point that an original preventive system becomes a reactive system..??

not sure whether I worded my question correctly..

Falconer,
in short is the 'kiss' principle a good idea?
many would say yes of course.others would disagree.In the end one can only judge by failure rates.
Whats more reliable, a s/w, a few relays, current sensors and a probe versus a clever box some wire s/w and a probe.
Done a bit of time on buses and I have changed a few PHC's.
I'd say more PHC's than failed probes on that type.
Most probes I've changed were the result of physical damage or altitude splits (in combo pitot /static probes as used on older 737 and 767 etc.)That is anecdotal evidence, you'd need to collate quite a history to have any scienctific conclusions drawn.

I'll leave any design critique to others that are more informed of the guts of the boxes in control. Been a while since I was on type and my notes are stashed somewhere.

What about a design change: connect the closed end of the Pitot tube to a high pressure pump. Whenever erratic air speed indications are suspected, push a burst of fluid via this connection to dislodge ice, dirt or leftover scotch tape.

Chance are that any attempt to blow a blockage off the probe would destroy the sensing device long before it managed to clear all but the smallest blockage. After all, it's the overpressure in the tube that's going to clear the obstruction, and that same excess pressure will be affecting the sensor.

It it ain't broke don't fix it.
 

Surely we should be asking "how do we prevent the pitot, a device that has accurately helped measure airspeed for decades, from icing up in extreme conditions"?

The pitot design is relatively simple and cheap (in comparison to some proposed alternatives) and it works.

I don't think that would be a workable solution. The amount of pressure required would be enormous in the case of a solid blockage - especially a plug of ice.

I once had to replace a pitot tube on a Bell Jet Ranger helicopter which was completely blocked. We suspected that the blockage was caused by an insect.

The maintenance manual specified that a maximum pressure of 20 psig could be used to attempt to purge a blockage (after disconnection all downstream sensors). We tried the procedure, without success.

It turned out that the tube had been blocked by a mud dauber wasp, which had built its nest within the tube over a 5-day period that the aircraft had been parked outside (in mid-summer) with no pitot tube cover installed.

Once the new tube was installed, we connected a regulated nitrogen tank to the old tube to determine just how much pressure it would actually take to clear the blockage.

We had to apply almost 200 psig of pressure before the wasp nest finally dislodged, and when it did, it came out like a bullet fired from a rifle.

The point being that trying to remove a solid blockage from air data probes with reverse air pressure would only be likely to cause major damage to the probes themselves, or to the associated plumbing - to say nothing of the extremely sensitive sensors to which the plumbing is attached.

JR Barrett

Some of the later probes such as the SmartProbe by Goodrich, don't require pneumatic lines or plumbing so there is less chance of a blockage.
http://www.goodrich.com/portal/goodr...SmartProbe.pdf

Obi

Its a great idea and certainly eliminates the web of tubing we have on many aircraft, BUT, it is still a pitot-tube except the sensor portion is built right into it instead of being remote in an ADC. I still like it though. If you want to have fun, try trouble-shooting a leaking system with the plumbing running all over the place.

"Amen" to that. I recently had a G-IV which had developed a serious in-flight data miscompare between the L/H and R/H air data computers. Ground testing quickly revealed a major leak in the static line feeding the #2 ADC.

We eventually found the leak to be caused by a cracked plastic B nut at the point where the static line feeding the #2 ADC connected to the R/H static port.

Fixing the actual problem took less than 30 minutes. Getting access to the point of failure however was another matter entirely. Six man-hours to remove the overhead ceiling panels in the entranceway to gain access to the tee fitting where the L/H and R/H static port lines joined together, (in order to isolate which side was leaking) - then an additional 35 man-hours of labor time to disassemble and remove the forward lav and galley, and then put it all back together afterward.

Remoted air data sensors are definitely a major improvement, which eliminate
a weak link in the classic "plumbed" pitot/static system.

JR Barrett

While you might say, such calculations are hard to do for a pilot, and noone memorizes a chart, there is one advantage of computer technology: Your computers can remember the weight, can run "SELECT" queries to look up data quickly and efficiently.

Where pilots are limited by how much math can do, how much data they can analyze, it might be possible to use computers to do the math. Both in case of calculations like this, and when predicting probable / possible future.

reversed airflow direction?
 

This gives me another idea... How about reversing the airflow completely, ie., push compressed air out of the sensor chamber continuously and measure the difference to the expected in-chamber pressure.

but if is just measuring expected air pressure (there is no free flow as such) why not do away with the pitot altogether? Just guesstimate it without all the convolution.No I cant see how it would work.

The aircraft must know what the immediate static and dynamic air pressures acting upon the aircraft are at any time and it must be accurate.

All sorts of bits on an aircraft are ice protected from pitot/static probes,angle of attack sensors, engine cowls, leading edges, windows, drain masts, temp probes,propellor leading edges engine intakes etc.Some electrically some by hot bleed air.
In general they work well.They must
The important ones are monitored for failures.Operations are limited if flying in icing conditions.
If there is a practical, sensible, affordable alternative that works better than the current type I would hazard a guess and say the manufacturers would be using it.
Newer aircraft have done away with much of the tubing which makes maintenance easier (less scope for leaks) but the basic needs have not changed.

I had a post deleated in R&N so rather halfheartedly posted this in JB. Despite everything, I think it's germane.

Skip the first couple of paras.


http://www.pprune.org/jet-blast/3759...ml#post4993312


The quote was well covered in a post earlier.

Could heated Pitot tubes be subject to vapor locks, i.e. hot bubbles of air/steam trapped inside and yielding erratic pressure measurements ?

vapour lock?
 

No I dont believe this could happen.

Piezo-resistive material could literally be sprayed on to the surface of the aircraft, facilitating multiple local pressure zones. The IAS could safely be calculated and the data could further be used for advanced anti-shake control and for computed compensation while flying in strong side-wind etc.

and when the skin ices up?
the pitot is simple its provides an accurate means to enable airspeed measurement.
I really cannot see what the fuss is about.
IF there is any link between with the air france prang and pitot problems it is likely a manufacturer issue not principle issue. In the vast majority of cases they work and work well.
Many critical parts of an aircraft have more failures than pitot probes.

The ice would still need to hold on to the piezo-resistive layer. Also there should be sufficiently many sensor zones so that it wouldn't matter if a few of them stopped working properly.


Edit - Removed sensor heating feature...:cool:

You could always ask the birds for the ''ps and 'q' because they know what they are doing!!!:}

seriously, keep it simple and safe


it seems we have left behind good simple thinking for all of the wonderful 'new ideas' in aviation like that bring'em down year after year for the same old reasons since 1903 :suspect:

and no I don't mean technological breakthrough or innovation we can't return venturi driven DG's on airbus or boeing airplanes, nor am I refereing to any accidents that remain unsolved

PA

Apple should start making airports and airplanes IMHO :)

A few nanometers thick layer of piezo-resistive skin could perhaps also be seen as an alternative ;)

Processing the data would require some dense continuous computing but this method should give a very reliable and precise IAS reading.

Until the present Thales/Airbus situation, pitot tubes have been very reliable.

It just shows that manufacturing even the simplest device can be screwed up. What could possibly go wrong with making and maintaining piezo-electric skin?

GB

vortex shedding
 

a few years ago I believe work was being done on speed sensors which relied on 'vortex shedding ' (why telephone lines 'sing' in the wind). These don't rely on dynamic pressure. Don't know what, if anything, became of them.

here you go...
 

1) 'Print' film with micro connectors onto the wing surface

2) Paint job

:)

The sensor surface shouldn't require any more maintenance than say a carbon fiber airframe.

...As a secondary and auxiliary meter, the IAS could be derived from an internal 3D reading of the wing geometry together with weight, static pressure and accelerometer data.

Pls tell me you are having a lend of us :hmm:
or from what galaxy you lobbed in from?:eek:

Ha ha :)

(I'm from Concerned Non-frequent Fliers Anonymous)

Advanced automation within aviation is the future and thus the need for a more sensible airframe.

Are you seriously suggesting to try to back out the external wing loading from FEM type measurements within the structure? That would require a degree of accuracy that simply does not exist, and may not feasibly ever exist in any cost-effective sense.

First, a piezo-resistive matrix on the wing surfaces would give data that eventually could be used to make flying in strong turbulence experienced as rather comfortable.

There would be a combination of inputs needed, with advanced realtime computing involved, surely. A carbon fiber airframe would have more flexing / movement that would make the measurements more 'visible' to the various sensors.

The main 3D physical motion of a wing could be measured from one strategic single point, affordably.

You can't deduce airspeed from the data you are suggesting, though.

At least, not with any expectation of accuracy.

A wing flexes the same under load to support the same weight, independent of airspeed (to a first approximation). So the wing shape at 100knots and the wing shape at 200knots would be essentially identical for the same weight. Even then, backing out the weight would not be trivial, especially given the unknowns of the inertia distribution due to fuel and payload distribution. (The wing flex for a heavy a/c with low fule state will differ from that with a high fuel load but correspondingly lower payload)

So, let's assume nevertheless that somehow we back out a reliable estimate for the weight. What's left in the lift equation - 1/2 rho V squared, S and CL. OK, S we can define, but to get closer to V we need CL. For that we're going to need an accurate model of the aerodynamics - not at all trivial, especially for an in-service aircraft not given the TLC a test vehicle gets. (Indeed, this methiod has been used with a KNOWN V to estimate degradation of CL compared to standard, and it's not always small).

I think if you do the error budgets in that process you struggle to get any kind of accuracy for airspeed - especially given that we have a pretty good way of measuring it right now that's a great deal simpler.

The alternative - Well, you could attempt to deduce the airspeed by looking at very small differences in wing loading due to low order Mach effects - not something terribly accurate at low Mach numbers. But that's even more error prone I suspect.

The model would be complex, and this 'synthesized IAS' could be thought of as a complementary reading, used when there was an eventual problem with the main meter.

The resistance will here be quadrupled and this will bend the wing accordingly.

The accelerometer data is meant to make the reading / the modeling more accurate.

(I dropped out of school long before any of the above and we only had access to an ABC 80 btw :bored:

A friend, John Talbot, has designed a simple system where a valve shuts off the ASI from the pitot tube and engine bleed air is blown back through the pitot system to the pitot head, clearing any ice, moisture, insects, etc. If this is done on each pitot head one at a time by a sequence system of some kind the ASI reading will not be lost.
The patent for this is now in the public domain so a developer would not have to pay royalties, etc. but I`m sure John would appreciate an acknowledgement. We have tried sending the idea to most of the manufacturers but no luck so far.
Publication number:
GB2418739
Publication date:
2006-04-05


Details can be found on

http://v3.espacenet.com/textdes?DB=EPODOC&IDX=GB2418739&F=0&QPN=GB2418739

No. Although the dynamic pressure is 4 times greater at 200knots compared to 100 knots, the wing loading is actually the same. Because the wing is supporting the same aircraft weight, and THAT is what causes the bending.

xMillion dollars worth of electronics being fed information by a couple of holes in the side of an aircraft.
I know its not as simple as that but its a question of balance.
Takes me back to my days in industry when the time and motion engineer would measure operations to the nearest minute then produce costings to a thousanth of a penny! He didn't understand the problem but common sense......
It is actually quite serious because we now have a very good indication that something wrong with these 'holes' can totally disable a large aircraft and that 'something' can be a problem encountered regularly by all pilots i.e. ice.

Why is it only Airbus receiving attention for multiple pitot problems?

l@ser...
 

Customs...... "The Traditional Monkey" ;)

P.S.: I wonder if it could be applied to machines somehow...

In industry terms, it isn't "only Airbus".

EASA Safety Information Bulletin 2009-17, issued June 09, contains "recommendations" to operators regarding unreliable airspeed procedures and the applicability is:

Now obviously the more general media are concentrating on AB because that's the simple story. And to be honest, would it really help matters if the press started harping on "it could happen to Boeing too, or Douglas, or ..."? There's enough unnecessary anguish already.