Instruments article feedback

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Instruments article feedback

Post by [email protected] » Sat May 04, 2019 8:00 am

Hi all

I have opened this topic for any feedback on instruments (electronic or steam) from my recent articles in the LA magazine. Of particular interest is calibration. With the potential advent of mandatory electronic conspicuity (CAP1777) and the new regulations on height clearance in controlled airspace (CAP 1779) we are becoming more dependent on accuracy of altimeters. Like many of you, I saved £1000 when I built and put in a non-certified altimeter then augmenting it later with an Avmap EFIS. As part of my research for my most recent article I put all my instruments through a test using an Air Data Test Set. I was pleasantly surprised to find all 3 altitude devices within scale tolerance up to 10000’. Now I know but what does that do for other pilots / controllers’ confidence Should the LAA impose a test?

Ian Fraser
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Donald Walker
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Re: Instruments article feedback

Post by Donald Walker » Mon May 06, 2019 11:20 pm

No.
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Chris Martyr
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Re: Instruments article feedback

Post by Chris Martyr » Wed May 08, 2019 1:52 pm

For day/VFR ?

Absolutely no !
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alioth
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Re: Instruments article feedback

Post by alioth » Wed May 08, 2019 5:40 pm

No. A test should not be required.

It should be the owner's responsibility to make sure their equipment is accurate enough, if they should fly places where that accuracy is needed. Not all LAA aircraft are flying near the LTMA or up and down the Manchester LLR. *Imposing* a test would be disproprotionate. How many altimeters are off by more than a trivial margin? I'd wager very very few. CAP 1779 (proposed harmonisation with SERA cloud clearances in class D) is also irrelevant in this case.
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Re: Instruments article feedback

Post by Chris Martyr » Wed May 08, 2019 9:01 pm

Whilst I fully understand that the replies seem to reflect a very emphatic , 'No' . It has to be borne in mind that 3 replies out of 7,700+ members may not be fully representative of how everyone feels.

I also understand that there are probably far more LAA'ers frequenting that other [red/yellow] forum than there are here . Only problem if it was put on there though is that you'll get every aviation expert in the world putting their 2p worth in . Which may not be quite representative of how most LAA members see this .
[email protected] wrote: I was pleasantly surprised to find all 3 altitude devices within scale tolerance up to 10000’. Ian Fraser
So Ian ,,,,,,,haven't you just answered your own question there .. :D
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Brian Hope
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Re: Instruments article feedback

Post by Brian Hope » Thu May 09, 2019 3:36 pm

OK Chris, I'll make it four against a test. Most LAA members fly in the up to 3000ft band of generally Class G airspace in pretty good VFR conditions. And let's face it, it isn't rocket science to check how good/bad your altimeter is against the stated QNH and your airfield elevation pretty well every time you fly. A millibar or two isn't going to make any odds and you can either adjust it out or compensate for it. If it is a long way out then it will be obvious and you can either have it looked at or bin it and buy a replacement.
Additional regulation should only be made on evidence of a safety case to show that it is required. Are Permit aircraft busting Controlled airspace floors or ceilings because of faulty altimeters, I think not, so until it can be shown that they are then let's leave well alone.
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Re: Instruments article feedback

Post by djwood » Thu May 09, 2019 6:10 pm

At the risk of being howled down, I do think that there is some merit in the idea. Here's why.

Personally I do much of my private VFR 'bimbling' far from controlled airpace where, frankly speaking, I don't really need any instruments at all for the purposes of avoiding airspace busts. And I would say that if any member is going to limit his flying in this way then there would be no need to ensure that the altimeter is particularly well calibrated, because it really doesn't matter.

However... few of us spend ALL of our flying well away from controlled airspace. Most of us go there sometimes. And, unless a pilot is going to be very dilligent about 1) setting his altimeter properly; 2) making sure that it is moderately accurate; and 3) giving himself a decent buffer in any case from airspace above (see the Take 2 initiative - 2nm and 200') then he risks infringing vertically. I do a lot of teaching around the Solent/Bournemouth area and I could not tell you how many times I've heard a tetchy exchange between a controller and a pilot, the latter of whom has inadvertently infringed by being a tad too high, albeit sometimes fleetingly.

Some time ago I did some work for the CAA through FASVIG (as was) looking at Infringement Management. One of the issues that was highlighted by that work is that no-one was then differentiating between vertical and horizontal infringement as they collected their data. So the real picture was and perhaps still is gloriously obscure. But my gut tells me that a high proportion (probably most, I suspect) of the brief, non-disruptive infringements are actually vertical in nature. Whilst I suspect that most of these are down to poor planning and/or distraction or whatever, some may also be down to dodgy altimeters. So, I think that there is some merit in the idea.
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Re: Instruments article feedback

Post by Chris Martyr » Thu May 09, 2019 8:03 pm

David . I certainly hope that any comment I make on this subject isn't construed as you " being howled down" . But I believe that Brian's comment re; setting airfield elevation prior to flight and then cross checking altimeter against GPS is a pretty good clue as to whether one is as vertically elevated as one thinks one is .. :D
Also , I'm sure that if my altimeter was lying to me , I reckon I probably would have had my suspicions raised and probably done something about it .
Isn't the best way of ascertaining this by getting a fellow airfield resident to set the same px setting whilst on the ground and then comparing altimeters ?

I really do not believe that recreational pilots flying day/VFR should be affected by this .
djwood wrote: I suspect that most of these are down to poor planning
And now you're getting to what really is the crux of the matter mate . These are the people I have no sympathy for whatsoever . The ones who want to go right up to that big old glass curtain but don't quite know where it is .....Then blame their instrumentation !.... :roll:

If you're a day/VFR flyer , then there are many common sense methods of ascertaining how accurate your equipment is . Regimentation / Compliance paperwork not req'd !

Oh,,and David . Nice Tiger Moth restoration there mate... :D
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Re: Instruments article feedback

Post by djwood » Thu May 09, 2019 8:09 pm

Chris Martyr wrote:
Oh,,and David . Nice Tiger Moth restoration there mate... :D
Thanks! I wish I could take the credit for it, but that would be wrong. It's a lovely aeroplane 'though.
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Re: Instruments article feedback

Post by alioth » Fri May 10, 2019 10:36 am

While only a few people of the membership have replied, I think it goes without saying that a lot of the flying membership of the LAA is flying with the LAA to get away from the suffocating hand of more and more things being imposed on us.

Imposing a formal test on the pitot/static system seems disproportionate for VFR: at least anecdotally, after 1500 hours of flying on many different aircraft (VFR and IFR, certified and uncertified, in the USA and in Europe), I have only encountered a single altimeter that was out of tolerance. This was my fault - because I dropped the thing. It was fine before that happened (and 300 feet off after being dropped). Needless to say it has become a rather expensive paperweight.

The other thing is to think about what would a test achieve. For example, testing the accuracy of an airspeed indicator: take the fully EASA and FAA certified Cessna 172 - testing its ASI around stall speed with a calibrated testing rig is pretty pointless. If you've ever stalled a Cessna 172, you will note the ASI reads almost zero when you actually stall due to the huge position error at high angles of attack (and in fact you can fly all day long nibbling the edge of the stall with the ASI reading zero). Many aircraft are similar (and the ASI will over read slightly at high speeds). The Auster pilot handbook for instance has a graph that tells you what the approximate error will be between actual airspeed and what the ASI actually shows.

The annual permit revalidation test is enough for the ASI, and we should be trusted to at least do a quick test of the altimeter every time we fly (setting QNH or QFE and verifying it's correct). As the crusty old Mode-C transponders get superseded by Mode-S units that can display pressure altitude, it shouldn't require a prescriptive test imposed on from on high to check this is right (and if you do have an old Mode-C transponder, then periodically checking it with ATC isn't a bad idea). More of us have multiple altimeters (eg. a mechanical one, an EFIS of some sort, and a trasnponder that will display pressure altitude) and any conscientious owner will observe that they agree.
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Clive Steer
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Re: Instruments article feedback

Post by Clive Steer » Fri May 17, 2019 8:34 pm

Hi All

In my view both the pressure instruments ie ASI and Altimeter used in aircraft are relatively simple in operation and reliable. However blockages in the pitot and static feeds either at the ports or in the pipes can produce subtle indication errors which may be missed and are hard to test for. The test set mentioned by Ian can be used for testing the instruments but are more often used to test for leaks in the Pitot/Static system plumbing. However the test set is poor at detecting blockages with the instruments in place. For instance a pitot port or pipe may show virtually no sign of degradation until it is somewhere around 90% blocked or possibly even higher as there is very little actual air flow. Given the sensitivity of both instruments more accidental damage can be done by mistakes made in testing than the instruments may experience in normal use. So best not to test and ensure the ports are kept covered except when flying.

To a certain extent an ASI is not an absolute instrument since its accuracy is also influenced by the position of the pitot port. Ideally the pitot port should be positioned so that when the aircraft is close to the stall the indication on the ASI is closest to the true air speed of the aircraft. The comment made about certain aircraft having a very low or no airspeed reading when close to the stall would suggest the pitot port is very badly positioned. With the pitot port positioned for best indication at stall the ASI may appear in error at cruise or higher speeds but the consequences of errors here are far less onerous.

An altimeter is again a fairly simple but delicate instrument which should give reliable operation. Having said that I've had two "Chinese" altimeters where one of the two vacuum capsules had leaked. In both cases the indications were grossly in error and couldn't be "zeroed" using the QNH/QFE setting knob. As has been suggested an altimeter can be checked by setting the altimeter to the GPS height before take off and checking for differences in the climb and this could be done when the aircrafts climb performance test for the annual permit renewal is done.

The most common issues with altimeters are caused and "cured" by vibration which frets the pivots and gears giving sticky operation under static conditions. In some of the best altimeters the gear wheels are gold plated to prevent corrosion and wear issues. Altimeter that have been dropped can be repaired and I have returned several to operation after checking in my vacuum chamber with a reference altimeter as well as a calibrated pressure transducer to cross check.

I would suggest that if at any time an aircraft instruments are removed the Pitot/Static plumbing is checked.

Clive

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Re: Instruments article feedback

Post by Chris Martyr » Fri May 17, 2019 9:24 pm

Clive . There is a lot of sense in what you have written . I am sure that you pretty much echo the feelings of many LAA flyers in what you say .

In which case then , may one assume that your response to Ian's suggestion ;
[email protected] wrote: Should the LAA impose a test? Ian Fraser
Will also be a ; 'thanks but no thanks'... :D
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Clive Steer
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Re: Instruments article feedback

Post by Clive Steer » Sat May 18, 2019 9:34 am

Hi All
Testing any device or system is only beneficial if it reveals any functional errors or potential failures that can compromise safety and the frequency of testing depends on the likelihood and consequences of failure.

Every time a pilot checks an aircraft before flight he is testing various system functions for obvious issues and this includes the instruments.

Checking if the ASI is giving a sluggish or abnormal reading during the take off run is a test of this primary performance instrument system. The annual Permit renewal stall test effectively "calibrates" the ASI to the aircraft and should show up gross error.

Testing that an altimeter QNH/QFE can be set tests this instrument and an error of accuracy in a Permit aircraft in daylight/VFR is unlikely to have a safety implication. However incursions into controlled airspace and flying in conditions where reliance on instruments is needed are different issues entirely.

So in my view given the ease of checking before use additional testing may be unnecessary and counter productive.

Clive

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Re: Instruments article feedback

Post by [email protected] » Mon May 20, 2019 11:16 am

The point I started with really relates to the potential consequences of the CAA’s latest plans for electronic conspicuity. If EC is mandated (as they say it will be), we will all be transmitting pressure altitude via either transponders or beacons. Under current regulations, any encoders (including those in CAP1391 devices) must have been calibrated to “the main altitude instrument for the aircraft” which implicitly must be calibrated to the EASA standard (because there isn’t another one). The EASA standard seems to me to be well over the top for what we want to do and could lead to a whole load of problems if it is imposed on us. I suggest there is room for the LAA to develop a much more “proportionate” standard which could be applied instead of the EASA IFR instrument rule.
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Re: Instruments article feedback

Post by dmcnicholl » Wed May 22, 2019 6:49 am

[email protected] wrote:The EASA standard seems to me to be well over the top...
No surprise there, it's what they do so well.
Donald McNicholl
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