21st century instrumentation

[AfricanSkies]

The recent Air Asia crash and, rightly or wrongly, comparisons to AF447 set me thinking.

Modern 21st century electronics have made it possible for amazing advances to be made in nearly all spheres or our lives. Aircraft fall behind because the pace of innovation far exceeds the speed of the certification processes required. Consequently aviation lags by years which these days represents a massive leap, sometimes by several orders of magnitude. This shortcoming will certainly be compounded in the future, in almost as exponential a fashion as the electronics are improving.

Totally new methods of doing many things are now possible, with well entrenched processes being thrown out on their ear and replaced by some newer, simpler and more effective technologies.

Consider aircraft instrumentation, based on pitot static systems which are prone to icing and other failures.

Would it not be possible to mount sets of accelerometers and GPS receivers at each extremity of the aircraft (wingtips, nose, tail) and thus be able to calculate the aircraft's true attitude in space, which could be displayed to the pilots as a 3rd person view? Without any pitot static information?

Instead of the INS's being located in one part of the aircraft and thus only able to calculate the position of the aircraft as a whole, with an inertial unit at each extremity the position of each extremity could be calculated and thus pitch, roll and yaw could be discovered. Almost like the position of four aircraft flying in very close formation.

in a calamity such as AF447 instead of the pilots being presented with conflicting, incorrect data and various alarms, a picture of the aircraft (in this case) falling through space with high nose up attitude could be displayed, clarifying the situation to the crew.

[Check Airman]

The issue of GPS for attitude information usually comes up after an accident. While GPS is good, it isn't good enough to be used as an accurate source of attitude information.

[mseyfang]

We use pressure altitude for a reason in that it correlates to aerodynamic performance, which is critical at each end of the performance envelope. So I won't go so far as to advocate using absolute GPS altitudes, no matter how accurate, as filed/directed altitudes for flight.

Now, that said, the idea of using such GPS data, assuming it is EXTREMELY accurate (i.e. +- about 6 inches), presents some intriguing possibilities as another source of data for pilots to determine attitude. I'm not an expert on this, but when flying pitch/thrust in an emergency, I doubt GPS has the ability yet to provide information with the precision required. However, it does have the potential to present an indication of extreme vertical speed, which would be valuable data to have in an upset. If we can get GPS data accurate enough to provide attitude data accurate enough upon which we can rely, it would be a good tool to have in the toolbox.

IOW, a thoughtful idea, but one which I question whether the tech is yet up to the task.

I'd be pleasantly surprised if someone can chime in and prove to me that my assumptions regarding accuracy are incorrect.

[NigelOnDraft]

Would it not be possible to mount sets of accelerometers and GPS receivers at each extremity of the aircraft (wingtips, nose, tail) and thus be able to calculate the aircraft's true attitude in space, which could be displayed to the pilots as a 3rd person view? Without any pitot static information?Can I ask what Pitot / Static Information has to do with calculating (displaying?) Attitude :confused:

[glum]

Ultimately an aircraft flies through the air, and it's behaviour relative to the mass of air needs to be measured. How will inertial or GPS data provide instantaneous airspeed?

[flapsupdown]

Great post for a discussion.

Yes, agree that the traditional pitot/static system is critical as it relays information required for aircraft performance. However, in the event of icing or system failure GPS information (if somehow made available) could save the day.

I don't buy the comment about the GPS system not being accurate enough - currently for GPS equipped aircraft, we can fly an RNAV approach with an RNP of as low as 0.3. 0.3NM!!! How is that not accurate enough??

In the event of a pitot/static system failure and/or unreliable airspeed, we can use the GPS groundspeed and wind information to help us. Furthermore, if they made the GPS altitude information available, though it would give us our true altitude - not pressure altitude or altitude corrected for temperature - it can give us enough information to respond accordingly. In such an extreme situation as complete pitot/static failure, even the trend (i.e. is the aircraft climbing or descending) would be enough for pilots to respond properly.

All the technology is there and available - just a matter of certification and getting through the red tape.

[Skornogr4phy]

0.3 NM is still considerably larger than the size of any airplane ever constructed. So unless you can get the receivers to know where they are in relation to the other ones on the aircraft, you would never be able to determine 3 axis data from it.

[aterpster]

flapsupdown:

I don't buy the comment about the GPS system not being accurate enough - currently for GPS equipped aircraft, we can fly an RNAV approach with an RNP of as low as 0.3. 0.3NM!!! How is that not accurate enough??

Make that RNP 0.10 for most modern air carrier airplanes.

[FiveGirlKit]

Unfortunately GPS/INS derived information does not provide all the information supplied by the air sensors on the aircraft to allow the aircraft to be flown safely, as aircraft fly relative to the airmass around them.


These sensors (pitot/static, Angle of Attack (AoA), Total Air Temperature (TAT)) provide information on what the aircraft is experiencing in the airmass it finds itself in. They are the only means to provide information that can be used by the automation or crew to determine if the aircraft is flying within its flight envelope (such as Airspeed, AoA, max pressure altitude). No GPS/INS sensor can do this.


Furthermore, aircraft instruments are calibrated for the ICAO standard atmosphere - to ensure that all aircraft fly to the same standard and so there are no conflicts due to altitude. This 'standard atmosphere' is based on pressure altitude and other compensations (such as temperature). It would take a significant global effort to change the concept of the ICAO standard atmosphere to mean GPS altitude, including changing the equipment fitted to every airworthy aircraft in the world.

[NigelOnDraft]

Yes, agree that the traditional pitot/static system is critical as it relays information required for aircraft performance. However, in the event of icing or system failure GPS information (if somehow made available) could save the day. I disagree, and this at the "root" of some of the problems we are seeing :sad:

Attitude Information is critical - without it we will (in IMC) quickly lose control. Speed is not critical - we can fly all day without it. Altitude / vertical speed depends on circumstances, and certainly loss of Airspeed and Altitude is an issue. However, we do already have GPS altitude as a (somewhat poor) substitute for baro altitude.

What is as critical as Attitude is maintaining lift, which in turns requires an AoA approximation. Hence if we set an appropriate attitude, and have level flight, we know AoA. Or put another way - fly level, and adjust power to get an approximate attitude, we are safe. The basis for any loss of ASI drill.

Trouble is the modern airline environment does not teach or practice attitude flying, but "chasing the Flight Director" and pretending that is Manual Flying :{

So you say, why not substitute GPS speed for ASI? Well fine, it tells us our speed over the ground, but has zero relevance to lift. Particularly since most of these ASI events seem to icing / CB related, where W/V alters dramatically. At heart is it better to have a "best guess" speed displayed that may well be dangerously wrong? Or remove the "invalid info" and make clear to the pilot it is invalid and they'd better make alternative arrangements.

I am firmly of the belief that "removing" dubious or invalid info is far safer than trying to cobble together a best guess. A read of the AF447 report, and any modern tech manual, I would venture to say shows manufacturers and certification bodies think likewise.

Go back to AF447. Lost ASIs. Had it just been flown level for a short while, ASIs would have reappeared, plug AP back in, carry on. We need to somehow (re)acquire those basic skills.

I reckon most aircraft, setup in the pattern without ASIs, at ~5nu will fly fine (clean), now reduce power, and when attitude hits ~7-8nu take a stage of flap. Will now need return to 3-5nu to fly level and slow again for next stage of flap when required.

When I, or my colleague are practicing a FDs off approach, it is noticeable that typically my colleague will call flaps purely with regard to the speed annotations (GD, S, F etc.). If the attitude for level flight gets high, and/or there is turbulence, or a turn / level off if I suggest some Flap there is complete confusion as to my concern - even though Alpha Prot has come up :ooh:

[AfricanSkies]

It may be that current technology is not up to the task we're discussing, but it may just be though. If not now, certainly soon. But now it should be good enough to give the crew decent gen in a calamity than the current state of the art, as emergency data?

Don't just put GPS unit on the extremities, put IRS units there too. I know its hardly a comparison to what will be needed, but imagine an iPhone on each wingtip, the nose and the tail. The accelerometer data is not for navigation, so 0.3 ANP etc isnt relevant. It's for attitude info only, realtime. The more accurate the GPS the better, and each system would complement the others and make it even more accurate.

Lets think a bit about this, we need..

EADI - derive attitude from the system I'm talking about (lets call it 3AE, 3 axis at extremities)

VSI - derived from GPS

ALT - derive from GPS

HDG - derive from GPS

ASI - derive anticipated airspeed (ie. What it would be if not acted upon by wind gusts) by calculating what airspeed should be at calculated attitude with known thrust setting at given altitude (temp you'll need a probe). Mach data by referring to temp and TAS (more about which to come!)

To adjust for immediate windspeeds, possibly use very accurate doppler radar which will reveal the speed of water particles in the air in the case of 'wet gusts' , and to measure the speed of dry gusts, the aircraft could issue a high pitched sound of a given frequency from the nose, receive it in the tail and wingtips, and using doppler effect calculations by comparing the frequency difference at reception could determine the speed of the air passing by the aircraft, like hearing a whistling train go by. I'm not sure how mach compressibility effects might upset this, perhaps someone here does.

Because a gust will not hit all parts of the aircraft simultaneously, if the 3AE system is accurate enough it would be able to compare how the airframe has responded in realtime to a database of known possibilities. Very very simplistically, if the left wing lifts suddenly before the right, and the aircraft then yaws left more than is usual and climbs, it compares it to the database test data which says, yes, that gust was from X bearing and direction. Speed of gust calculated by micro-time between motions of extremities.* We're talking vast computer power here, but it is available. The latest mobile phone chip can do a teraflop of throughput, which is what the worlds fastest supercomputer could do in 2000, only 14 years ago.

Combining these different results with each other will make the final result more accurate, as will analysing instantaneous changes in groundspeed (GPS) and adding that to the mix. The clues are all there, we just have to link them all up like a high speed detective case. Sounds silly but thats essentially what it is.

There we have our blind flying instruments back.

We know the crew shouldn't be faced with conflicting data and spurious alarms. If crucial data is lost, or if the data falls in the defined to be rubbish category, the computer needs to make up for its loss and not either just jack it in or pull some dangerous kneejerk move. At worst it needs to do nothing and display "Stand by!" leave all controls in last setting including engine controls, and display the known required pitch attitude on the EADI for that power setting for level flight at the aircraft's altitude and weight until the crew make a decision and intervenes, or good data returns.

The 3AE system could display the aircraft from a 3rd person view, in 3D as a friend of mine on here recognised. The pilots could watch themselves spinning. (Airline livery obviously a manufacturer extra!) You could even view yourself landing it from a lateral perspective. Its really now just a big computer game with a real plane attached, all the data is there, we just couldnt use it before because it took such processing power, and such accurate instruments. It may not surprise some of you that nowadays its possible to take photographs at a rate of one trillion frames a second, fast enough to freeze a photon. There's yet another solution to the no pitot tube problem - measure the progress of particles in the airstream using this technology...we're back to casting a log overboard and measuring the knots:p

[pulse1]

Sorry to butt in but I distinctly remember reading a flight test report where they used differential GPS to determine attitude.

Something like this:
Space flight tests of attitude determination using GPS - ResearchGate (http://www.researchgate.net/publication/227866159_Space_flight_tests_of_attitude_determination_using _GPS)

[AfricanSkies]

Thanks for that link. So they have done it already :OdI'd like to read the full article but it seems you have to register. Amazing isn't it, sub centimeter accuracy! And here we are cutting the edge with 0.03 ANP:sad:

Another thing that I'd like to think would be useful is a Vref call out, maybe we can apply for that instead?:p

[Peter H]

Amazing isn't it, sub centimeter accuracy! And here we are cutting the edge with 0.03 ANPI was with you up to the last sentence.. The sub-centimeter accuracy refers to what is essentially a differential GPS system, while the
0.03 ANP relates to an absolute GPS position.

Differential GPS is always going to be a lot more accurate, as lots of error mechanisms cancel out (e.g. variable ionospheric effects).

[phiggsbroadband]

I am not to sure that the inbuilt error of each wing-tip GPS will be the same, unless they are synchronised together.
At the moment I have my GPS telling me where my car is (it's parked on the drive outside the house.) and it has given readings of 55,44,40,43,50... feet away.
So what sort of calculations can you do if the Starboard-Wing GPS cannot accurately measure where Port-Wing GPS is.?

[NigelOnDraft]

ASI - derive anticipated airspeed (ie. What it would be if not acted upon by wind gusts) by calculating what airspeed should be at calculated attitude with known thrust setting at given altitude (temp you'll need a probe). Mach data by referring to temp and TAS (more about which to come!)

To adjust for immediate windspeeds, possibly use very accurate doppler radar which will reveal the speed of water particles in the air in the case of 'wet gusts' , and to measure the speed of dry gusts, the aircraft could issue a high pitched sound of a given frequency from the nose, receive it in the tail and wingtips, and using doppler effect calculations by comparing the frequency difference at reception could determine the speed of the air passing by the aircraft, like hearing a whistling train go by. I'm not sure how mach compressibility effects might upset this, perhaps someone here does.I think you've truly lost it :( If you presented this rather complex solution, with numerous inputs all liable to failure and error, I am sure the boffins would listen carefully... and then one would say "but we could just stick a tube into the air facing forwards?"

I'm really not sure why this pressure for a GPS derived "attitude"? Modern INS units are amazingly reliable, we have 3 of them, and even after internal failures, the attitude function is retained. Whereas any GPS derived solution is vulnerable to Uncle Sam just throwing the switch, and/or jamming? Can you think of a modern airliner accident caused by an attitude display fault? Since the STN 747 which was a mechanical instrument, and even then, the other 2 indicators were fine IIRC?


PS I think your Doppler thing will only work when the tail falls off :8

[Denti]

Don't just put GPS unit on the extremities, put IRS units there too. I know its hardly a comparison to what will be needed, but imagine an iPhone on each wingtip, the nose and the tail. The accelerometer data is not for navigation, so 0.3 ANP etc isnt relevant. It's for attitude info only, realtime. The more accurate the GPS the better, and each system would complement the others and make it even more accurate.

Why in gods name would we need something as complicated and failure prone as that when we have three excellent laser gyro driven IRS already which provide attitude information? And a fourth attitude source in the backup instrument?

Attitude information is not the problem, flying the correct attitude is.

And differential gps is all nice and dandy, but it usually requires ground equipment in a short range. Google GBAS and have a read of a real world approved and certified differential gps application in aviation.

[pulse1]

As I understand it, which isn't saying much, but you only need a ground station for DGPS if you you need pin point accuracy in relation to the ground, as in a GPS approach.

For monitoring attitude for an aircraft, the base station would be on the aircraft.

[underfire]

Wow.

A few issues broaught up...

1. Pitot tubes, there are at least 2 one in the front facing forward, and one in the rear facing backwards to airflow. The resultants are coupled.

2. DGPS does rely on ground stations, and is very localized. One must understand that DGPS corrects to the WGS84 ellipsoid model. It is accurate to that model. That model is an approximation of the Earth, so in effect it is accurate to an approximation, which, while getting better, has issues with the bulge of the Earth, especially in the northern/southern latitudes. In addition, I have seen little information on the broadcast range that would make this viable for aviation.

3. As noted before in other threads, the GPS tells the aircraft where it was, not where it is. The Kalman filter is used to estimate where the aircraft is. Due to latency in the GPS signal itself, onboard processing, and other issues, the Kalman filter is required to estimate current position of the aircraft. For reference, a single GPS broadcast from one sat is about 3 seconds long, you need at least 6 for any accuracy, and the sats are not sync'd. Thus in effect, the INS, not the GPS is giving you the current position.

4. Altitude. Depending on the system architecture, the GPS is giving you altitude based on a reference from the horizontal position to the WGS 84 geodetic/ellipsoid. Some units calculate altitude based on actual calculations to the ellipsoid, while others have a simplistic grid placed over the geoid, with a lookup feature. This is more accurate when flying a straight line (and from above) at a constant speed. The system is less accurate in turns, depending on how the individual system architecture calculates geoidal position in a turn. Again, as noted in other threads, the FAA procedure design software did not , and still does not, do a very good job of approximating location while the flightpath turns on an elliptical surface.

5. As Denti noted, GBAS/GLS capability. Localized ILS like guidance. Why this is not on every runway end, and on every aircraft, I just dont know. A failure of the regulatory system is about all I can determine.

[island_airphoto]

I must be totally missing something.
ATTITUDE is displayed by gyroscopic instruments.There is no need at all to put a GPS at each corner of an airplane.
Here are some examples of fine and dandy attitude indicators you can buy today ;)
http://www.pilotfriend.com/training/flight_training/fxd_wing/images2/16.jpg
This one is even portable and shows GPS groundspeed too:cool:
http://sarasotaavionics.com/images/productimages/DYNON/D1a.jpg

[*Lancer*]

Attitude already comes from the IRS in aircraft so equipped. Gyro is only the backup (standby attitude).

Airspeed and Altitude must be referenced to the actual atmosphere being flown through. You're flying through air, not space. Spacial reversion is the backup already (BUSS/GPS).

The issue is recognising an instrumentation problem, and being able to ignore the suspect data and revert to backup source.

You're right though, some fresh thinking is probably useful!! :ok:

[underfire]

I have seen prototype units that use the Microsoft kinects pixel recognition system, and the iPad gyro chip. The kinects unit was especially hyperaccurate with true unbounded 360 spherical pixel recognition capability. It tested far more accurate and reliable than the laser gyros...
The units were being set up for underwater use, which has far greater needs than aviation due to lack of GPS update.

[Australopithecus]

What perceived need are you purporting to address with this thread? As has been already mentioned, and should be abundantly clear, raw attitude information is available on all three sources in an airliner. Physically separating sensors in space does nothing for their sensitivity, nor their accuracy.

If you wish to pretend to be on the cutting edge of ergonomic thinking spend some time pondering how a modern stall warning should look and sound. And how mode reversion should be annunciated and summarised on an ECAM system. And how, for god's sakes, alpha can be intuitively displayed. Along with stall alpha corrected for altitude, mach number, mass and temperature.

While you are at it figure out how to get Airbus to permanently display flight path angle so that gamma can easily be ascertained.

[underfire]

Its part of the next generation of IRS systems.

That clear it up for you?

[darkroomsource]

Whenever I hear something like "we should convert to X because it's so much better than Y", I am reminded of what happened to Henry Ford.

He had to decide on what kind of engine to use for his new automobile. He had several choices, including electrical, steam, diesel and gasoline. Steam was discounted for inefficiency, electrical for battery capacity (still an issue), so it was down to diesel and gasoline (petrol).

Furthermore, he could choose between using petroleum diesel and bio-diesel, as both were available and usable at the time.

When looking at all the options, gasoline turned out to be best because
a) it was far cheaper than diesel (it was a by-product of making diesel)
b) it was far more available than bio-diesel (vegetable oil was harder to make in quantity at the time than diesel)
c) it cleaned up the environment because gasoline was being dumped as a waste product of making diesel.

So, the best solution at the time, cheaper and greener (using up all that waste gasoline) was to make his car use a gasoline engine.

Now, a hundred plus years later, it wasn't true, it's not cheaper, and it's certainly not greener.

Pitot tubes, vaccum gyros, pressure altimeters, and little balls in a curved tube of glass have been proven successful at giving the pilot sufficient information to keep the shiny side up, and continue to work if the electrical system stops working.

[AfricanSkies]

ENIAC worked. But that didnt stop us from designing better computers. 50 years ago not a soul envisaged you'd be reading your instruments off a a television whilst blind flying. I just think that with the pitot tubes out of the way life would be safer. They can be iced up, crushed by airbridges, blocked by insects or debris, damaged in many ways, easily and without such damage being very apparent.

Anyway I'm not trying to be smart here, just to throw ideas around, even if they do seem way out. Because the world of technology is improving at a pace where the exponent seems to be exponential itself and many new ideas outside of aviation could well benefit aviation very much if we heed them.

Imagine you were transported 50 years ahead in time. Not into a world where all modes of transport are unrecgnisable, just far enough that were still working with the same stuff, just improved, as we have improved upon the last 50 years.

Think of the jetliner docking at the terminal, raising its nose door and having the entire load of passengers withdrawn in their pod, a pallet which looks like and is in fact the inside of an airliner. Whilst refuelling takes place, a fresh pallet with new pre-boarded passengers, their baggage, clean toilets, full galleys is loaded and the aircraft is turned around in 15 minutes. Perhaps with a cargo pallet. Or a cargo half pallet and a passenger half pallet.

All clearances and comms via computer, no radio comms except with engineer. FMSs sort themselves out. No more computer to paper to computer via crew. Aircraft pushes itself back and is started automatically at optimum point. Aircraft displays taxi clearances, infrared cams see through fog.Separation much tighter, autopilots receive guidance from ATC systems, no more corridors and airways. Much better FCS (we're learning more about this right at this point with another loss of control accident in Air Asia) and foolproof instrumentation. Because if the computer fools the pilots as it does now, how can they be blamed for crashing?

Yes, I might be dreaming but thats what I intended this thread to be about... imagining the next state of the art.

[darkroomsource]

Yep, there are lots of ways to make improvements.
But until there's a sensor that can tell airspeed without using a pitot tube, you're going to need a pitot tube.
Airspeed and ground speed are not the same thing.
Knowing your ground speed is what non-pilots want to know, and pilots need for planning arrivals, descents, etc., but airspeed is needed for fuel flows, stall speeds, etc. (granted, the pitot tube method isn't perfectly accurate for stall speed, but we still don't have anything better, after a hundred years)

[AfricanSkies]

I think having a high frequency sound transmitter in the nose of the aircraft and receivers in the wingtips and tail would work. Measure the frequency shift and you have the airspeed. Like a train whistle going past you..doppler effect. In effect, youre sending something (sound) into the medium youre flying through (air) and you're measuring its progress. Distance and absolute speed are known, time is calculated, airspeed can be derived?

[DozyWannabe]

...in a calamity such as AF447 instead of the pilots being presented with conflicting, incorrect data...

The pilots were not presented with "conflicting, incorrect data" in the case of AF447 - they temporarily (as in for less than a minute) lost airspeed data. Everything else was working fine throughout the initial accident sequence.

If you're referring to the Stall Warning cutting out while the IAS data was NCD and reappearing when nose-down was applied, then with respect it's fair to point out that a pilot who is well-versed in basic aerodynamics should know that said scenario indicates an issue with the Stall Warning system, because it is physically impossible to go from unstalled to stalled by reducing AoA. It's also worth pointing out that by the time the aircraft ended up in this state it was already too late to effect a recovery.

The problematic Thales AA model pitot tubes were already slated for replacement when the accident happened, and since they were replaced there has, to my knowledge, been no more incidents of triple pitot tube failure on the A330 or A340.

[BARKINGMAD]

Cut&Pasted from my posting in the AirAsia thread.

Old CFS dictum for Straight & Level 1 and subsequent flying lessons;

Select (attitude) Hold Adjust

Power (Thrust) Attitude Trim.

What is new in aviation when things are beginning to get out of hand, literally and figuratively? Or has this piece of basic flying training been edited out in favour of Magenta Children easyspeak?

Airbus may have its various Laws, but the Laws of Physics and Energy Management were applicable and immutable long before Alphonse and colleagues decided to make 'their' aircraft allegedly foolproof.

It is early days but if this accident resembles/mirrors/copies AF447, then what are the civil aviation training regimes doing/are going to do about the tendency for LOC at altitude, assuming AirAsia still had wings and stabiliser attached for the use of the crew??!!

I note a stunning lack of response, beyond one admission, to my request for reports from those who've actually handled their craft at high masses at max altitude.

Probably this specific topic belongs as a separate thread under Tech Log, but I'm still concerned at the lack of reports either way.

Tin hat donned in anticipation........................

Why are so many on this forum obsessed with new shiny hardware solutions which will not be fitted to ALL airframes til long after the next few high-altitude LOC accidents? :)

[grounded27]

The issue of GPS for attitude information usually comes up after an accident. While GPS is good, it isn't good enough to be used as an accurate source of attitude information.


GPS with IRU's mounted at 2 to 4 (nose and wing tip or all 4 points) points could be a great source of attitude information. When I say IRU I mean RLG and accelerometer updated by GPS, could be very accurate.

[grounded27]

Hey? What the hell ever happened to pitch and power? This accident and AF give me the feeling that the problem is culture and training. Thousands of hours sitting in a seat with otto the pilot connected to the FMS with no real issues have changed pilots from what they were 20 years ago. It gives me the thought that pilots spend more critical time during an abnormal event evaluating information and flipping through a QRH than simply reverting to pitch and power to drive through extreme circumstances. Is this not possible in the A320.330? I would expect that the PF should do this while the PNF rolls through procedure to evaluate all the warnings and QRH.

[BARKINGMAD]

grounded27,

I'm trying to make the same point but in different words, but I get the impression we are breaking wind in competition with thunder??!!

I don't know the status of most of the posters on this topic, a lot must be "simmers" or trolls or it depresses me seriously to think that some of the :mad: posted is serious comment from experienced aircraft operators, who used to be known as pilots.

On my transition from military to civilian aviation 28 years ago, I recall being lambasted by the TC in the sim as I converted my brain from basic B&W artificial horizon instrument flying and was forced to slave myself to "the bars", even though I was FLYING the beast to the required accuracy. That type of TRTO conversion instruction is obviously not a new phenomenon, but fiddling with & following the APFDS system seemed to be an over-riding priority for that fleet chief trainer and others since then .

Others on these forums have and are calling for more BASIC flying as part of type conversion courses, but TCs have to follow whatever menu has been prescribed by the relevant xAA and Company.

Yet again a deafening silence from the AAs on this topic, presumably they need something like another few accidents and some media pressure before they will change their tune? :ugh:

[*Lancer*]

BARKINGMAD and grounded27, attitude information already comes from the IRS!

[FullWings]

Is the world crying out for inertial sensors in aeroplane wingtips? No, not really - the ones we have in the fuselage work fine, thank you. Anyway, I don’t think they would add much to accuracy as the wing flex on large airliners would see them pointing all over the place in turbulence.

As others have said, attitude/position reference technology is mature and not in great need of improvement. What might be is the presentation to the pilot, which hasn’t changed much in commercial aviation since instruments were first built. But that’s another topic entirely.

Probably what has set off this discussion are recent incidents/accidents involving loss-of-control following errors in pitot/static/AoA sensing systems. Most aircraft this side of FBW military ones will fly quite happily without having to “know” what their airspeed is. Having a set of wings and a tailplane bolted to a fuselage in the conventional manner leads to an aeroplane that has enough static/dynamic stability to fly itself most of the time, like a well-made paper dart.

Once you start adding software protections against things like overspeed and stalling, you become vulnerable to sensor failures. Very, very rarely, the systems that for 99.9999% of the time do an exceedingly good job of keeping you safe and sound are now actively trying to kill you. No wonder it comes as a bit of a shock to many when this happens. Yes, there are memory drills for power and attitude that if executed in a timely and correct fashion will turn it into a non-event. The problem lies in actually diagnosing the issue(s) correctly in the first place and taking back control of the aircraft from the systems that are no longer performing their function correctly. As (bad) luck would have it, the most likely time these systems are going to freak out is not in a clear blue sky with an uninterrupted view of the ground but in the middle of a thunderstorm at night, where pilot workload is already high.

The 777/787 have a convenient switch just above the head of the captain. In an Airbus, you have to pull a selection of circuit breakers, so I’m told. The effect is to return these aircraft to something that relies on aerodynamics and basic controls to fly rather than computer augmentation. There are a further set of CBs to pull if you can’t get the myriad of warning systems, now working on false data, to shut up and let you think.

It’s a problem and it’s not going away. However, most agree that the day-to-day benefits of FBW far outweigh the ultra-rare occasions that it dumps you in the mire. Doesn’t mean that we shouldn’t be trying to solve the problem from all angles, though.

[BARKINGMAD]

"BARKINGMAD and grounded27, attitude information already comes from the IRS!"

I believe I was aware that after a few years on INS/IRS equipped aircraft that this is indeed the case.

So your point is? :confused:

[*Lancer*]

Sorry, read your post in conjunction with grounded27's earlier comments. Out of context.

[Oktas8]

A note about GPS attitude.

It is perfectly possible & cheap to determine attitude from multiple GPS sensors. It doesn't depend on absolute position in space but on the different phase of a single GPS signal, as received by two or more sensors about 5 to 10 cm apart. They don't know precisely where they are relative to the earth, but they do know position relative to each other. Using this technique, cargo ships for example can generate a true heading accurate to about a fifth of a degree.

The reason it hasn't taken the aviation world by storm is partly due to continuity & availability of signal, and partly due to the lack of a signal when you're inverted!

None of this improves the recent LOC accidents, as every airliner is well served with accurate & very expensive redundant RLGs for perfect attitude sensing. Whether the pilots can use attitude intelligently is not a given....

[Denti]

Using this technique, cargo ships for example can generate a true heading accurate to about a fifth of a degree.

Wouldn't that be a true track?

[jtt]

I think having a high frequency sound transmitter in the nose of the aircraft and receivers in the wingtips and tail would work. Measure the frequency shift and you have the airspeed. Like a train whistle going past you..doppler effect. In effect, youre sending something (sound) into the medium youre flying through (air) and you're measuring its progress. Distance and absolute speed are known, time is calculated, airspeed can be derived?There's nothing the Doppler effect will help you with here. It's due to a velocity difference between the sender and the receiver and doesn't depend on some surrounding medium (which isn't even needed, the Doppler effect can also be observed with light in vacuum - that's e.g. how astronomers measure how fast other stars are moving away from us). So all this proposed device would tell you is that the wings are starting to move at a different speed than the nose cone. But that probably will be noticed by the pilots very quickly anyway.;)

Perhaps you mean some kind of device that emits "pings" and you measure the time they need to arrive at the receiver? But that would require the speed of sound to depend on the speed of the medium, which it doesn't. It doesn't depend on the speed of the source - otherwise you wouldn't get a sonic boom - so it also can't depend on the speed of the medium.

[PJ2]

Barking Mad, re, "Why are so many on this forum obsessed with new shiny hardware solutions which will not be fitted to ALL airframes til long after the next few high-altitude LOC accidents?"

Not only will they not be fitted for years, but the instrumentation is already available and installed. The key is in knowing one's aircraft and systems and using them correctly, bearing in mind that no installation is perfect in preventing accidents.

Let us look at some of the examples which may be driving this desire for "new" instrumentation, and why I think that such a drive is focussed in the wrong direction.

AF447
The key to AF447 as we know was to "do nothing", except maintain thrust and pitch attitude. The airplane was already stable; a loss of airspeed indication does not affect airflow over the wings or engine thrust.

Some systems will be lost of course. In such a case, one must slow down, respond with measured actions, then first of all aviate which means stabilized the airplane, (even if here, that meant "doing nothing"), then deal with the ECAM or EICAS and the loss of airspeed indication(s), for which there is the UAS drill including Airbus directions as to when to apply the "flight not at risk" section of the UAS drill, (which states that pitch and power must be maintained and not changed, while values for those two metrics are looked up in the QRH).

A loss of airspeed indication at cruise altitude, in and of itself, does NOT put flight at risk and it is NOT an emergency - it is an abnormal. Thirty-one other A330 crews faced this problem successfully. I would not say the "cause" was the loss of speed information but the absence of SOPs and cockpit discipline. No set of new technical gear or software is going to fix what was/is a training and checking matter.

UPS1354
If "new, improved" instrumentation is desired we might include something that may have prevented for example, the UPS A300 accident at Birmingham - a "side-view" of the approach showing the aircraft's actual height above ground, with a display of actual terrain, (from the EGPWS database).

Certainly there was crew fatigue involved and FAA regulations which do not consider cargo aircraft crews as susceptible to fatigue like passengers crews are. But the fact remains that non-precision approaches such as the one which resulted in this accident (because the crew was late in getting the GNSS approach in and the airplane didn't capture it), are higher-risk approaches, and a "side-view" horizontal situation would have made a difference, particularly if predictive arcs were present much as they are in the NAV displays of the B767/B777/Airbus series, etc. when descending to a set altitude.

Airbus BUSS
The Airbus "BUSS", (Backup Speed System) only works at/below FL250 due to Mach Number effects on stall AoA, (which are much lower at cruise Mach Numbers). One must still know the drills and know one's airplane.

As an aside, it will be well worth establishing why the QZ8501 crew was not able to recover a very-likely-stalled aircraft. What was unavailable to this crew and what did they do to try to recover? AF447 was recoverable with sustained, (about 50"), full-ND stick, even moreso in lower, thicker air. (I'm not re-arguing anything here, just trying to understand why the notion of "new" technology has legs.

[Denti]

UPS1354
If "new, improved" instrumentation is desired we might include something that may have prevented for example, the UPS A300 accident at Birmingham - a "side-view" of the approach showing the aircraft's actual height above ground, with a display of actual terrain, (from the EGPWS database).

Dunno, i have been flying around with exactly that for the last 8 years or so in my old fashioned 737. Now, on the much more modern A320 that is not available at all, in general the ND/PFD is IMO better on the boeing, but both work and are enough to fly safely.

[PJ2]

Denti - certainly the changes I mention are not necessary for safe flight. The original argument was "new-stuff = safer flight" and I don't agree with that premise - what we have is doing the job. Appreciate the feedback on the "side-view" tho'...I hadn't spoken to anyone who'd used the display.

Under the heading of "knowing one's airplane" and the fact that you say both are sufficient to fly safely, with which I agree, (I flew the A320/A330/A340 and they didn't have the "side-display" but it was never an issue), the argument for "new instrumentation" is to me, moot.

Out of interest, are you flying the classic or NG?

[Denti]

I started out on the classic (500/300) and then transitioned to a mix of classic and NG (700/800) until the classic was phased out. No we're phasing out the 737 altogether for the A320 which was our second fleet for the last 10 years or so anyway.

Most colleagues don't use the VSD (vertical situation display) much, but i grew accustomed to it and used it during approach and departure. It doesn't only provide a side view of the terrain, waypoints and restrictions, but an energy state view as well. And the added bonus is of course that one can have both a terrain and weather radar display at the same time, which is impossible with the usual depiction. Only downside is that the sideview of the terrain follows the current track, not the "magenta" line like it does on the 787.

I believe airbus copied that thing and it is available on the A380 and A350, but won't be retrofitted to the older planes. Then again, they all have very tiny screens to begin with and probably taking some away for a VSD wouldn't improve the overall display.

[Tscottme]

IIRC, Embry-Riddle demonstrated use of GPS to determine attitude. I think they outfitted a single-engine Piper with GPS on nose/tail/wingtips. I don't remember results of study. The story I read was in AOPA magazine or AWST. It works well enough IIRC.

[megan]

I think they outfitted a single-engine Piper with GPS on nose/tail/wingtipsA PA-28. Such was the accuracy they were able to measure the flex at the wing tips due loads imposed on the spar.

[AfricanSkies]

jtt, thank you for a very interesting reply and for helping me straight on that.

I'm not sure I understand your last about the speed not depending on the medium, or the source. If you could elaborate a little on that please? In the case of pings, say nose to tail, if the temp and density of the medium, air, is known, would comparing the time difference between the expected static speed of sound in air at that density vs the measured speed of the ping give us the speed of the medium? Which is the airspeed?

Thanks for your input:)

[Uplinker]

The radome of an airliner is attached to the fuselage with a number of fixings, (four?). If each of these incorporated a strain gauge, then the dynamic pressure of the air on the radome as a consequence of the forward motion of the aircraft could be measured and converted to an airspeed. In theory, this system would be immune to icing and insects etc., since there would be no holes or pipes which are prone to blockage.

And/or you might be able to make a similar measurement on the slats, or the fin mountings.

I wonder if this would be accurate, sensitive and stable enough to give a useable IAS readout?

[jtt]

I'm not sure I understand your last about the speed not depending on the medium, or the source.Me neither anymore;-) (Sorry, BTW, for the long delay, but I hadn't looked at this thread for some time.) Actually, the speed of sound does not depend on the speed of the source, that's where I got it right, i think. But it's constant relative to the speed of the medium, so sound produced in air moving at 100 miles/hour would move faster in the direction the air is moving than in the opposite direction. Thus something like a device making "pings" and measuring the time the sound takes to arrive at some other part of the airplane in principle should be feasible (as far as I can see, but, as you've seen, I can be wrong;-)

The problem I see is that the speed of sound depends on (at least) three things: the temperature of the medium, the pressure and the its composition. Temperature and pressure already get measured (but I don't know if the precision would be sufficient). But you also need to know the amount of moisture in the air (or even if there are water droplets). And that might be harder to measure, especially if flying into and out of clouds at rather high speeds. Where such a device might come handy would be in situations where there are conditions leading to the pitot tubes clogging up with ice, i.e. conditions where there's quite a bit of moisture (perhaps super-cooled water?). And measuring reliably and with sufficient speed the exact composition of the air you're moving through to arrive at a good enough estimate of the local value of the speed of sound might pose a bit of a problem.

One possible solution might be to measure the speed of sound directly and independently by having another "pinging" device perpendicular to the direction of flight (assuming that cross winds aren't too large to mess up everything). I.e., measure, for example, the time it takes a ping from the tip to the root of the wing to arrive at an estimate for the speed of sound at that moment and use this for calculating the speed of air in the direction of flight. Unfortunately, that could make the device twice as expensive (and double the likelyhood of failures;-)