Steam-navigation versus GPS failure rates

[Nipper2]

I'm interested in the relative failure rate of old steam (gyro driven instruments and DME, ADF and VOR) versus GPS. Who has had failures of what, and and what rate per flight hour?

I'll start things off. I have flown about 250 hours in various spam cans and suffered two total gyro instrument failures. One non-erecting AI discovered at the pre-flight check stage (prior to departure for an flight in IMC) and one HI that failed in flight precessing at a sufficient rate to make it useless. One pump had sufficiently poor vacuum that it was entered as a defect at the conclusion of the flight.

I have had one failure each of DME and ADF and an unservicable GS though the localiser continued to work.

Combined time on Spam Cans and LAA types of about 450 hours with both panel-mounted GPS and hand-held devices has so far scored a zero failure rate.

How have other people fared?

[IO540]

Hard to get good data on this.

There are good avionics, and there are crap avionics, and all in between. Even within one manufacturer's range you get some good vintage and some real dogs. And hangarage v. outdoor parking makes a difference, although the data on this is not conclusive (IMHO largely because the owner rarely gets feedback on the actual fault).

I've not been kicking around GA for many years, but it seems to me that

- most ADFs are crap, except the Bendix/King KR87 which is very reliable

- most Narco stuff is crap

- the late-1990s-designed Bendix/King (Honeywell) stuff like radios (KX155A/165A), GPS (KLN94), DME (KN83), HSI (KCS55 etc) is pretty reliable, while their autopilot from the same era (KFC225) are hugely unreliable

- the newer GPSs (Garmin 430/530) are pretty reliable

When I used to rent spamcans, must of the stuff in them was duff but the avionics were all old - mostly 20+ years. This is not suprising since I don't think you will get a 20 year life across the board of avionics, by a long way, in a plane sitting outdoors all year.

The Avidyne glass cockpits get very mixed reports, with many crashes of the software especially in plastic planes. The G1000 seems to be a lot better but IMHO it is too early to tell re long term reliability in humidity etc.

Vac pumps do go, not if but when, and sometimes gradually and sometimes spontaneously. I changed one at 700hrs which did not make the green arc below 1000rpm.

[Rightbase]

VFR Cambridge to Blackpool, Netherthorpe-POL leg.

NAVs on POL and GAM, plus hand-held GPS. I'm aiming for a small gap between controlled airspaces, so belt, braces and safety harness.

GPS failure - I had stored POL as a waypoint but not included it on this route (:ugh:) so the GPS wanted to take me direct from Netherthorpe to Blackpool. GPS binned for post flight investigation (and GPS route corrected for the return flight!).

Not really a GPS failure, a planning failure. But a serious warning that different technologies have different failure modes and risk factors.

Needless to say my GPS routes are now double checked (as are waypoint coordinates). But I'm only human.....

I have seen GPS interference test notams; I have seen compass errors and NDB/ADF malfunctions, and I've seen VOR unavailable notams. I have not yet flown on a day when a DME service was unavailable, but that is probably an accident of my flying diary.

Nothing is infallible, not even the pilot. Always have a plan B!

[julian_storey]

I've had a vacuum pump go on me whilst in cloud approaching the Channel Islands in a Cherokee. Had to descend through cloud on the (electric) turn and slip / compass. I've also had a NAV box pack up on me just as I was trying to intercept the localiser on an IFR flight into Geneva.

My personal GPS usually seems to loose signal on the South Coast between Selsey Bill and the Isle of Wight.

Rather than see some kind of almost tribal argument develop between those who like to use GPS and those who prefer to use traditional radio navigation aids, I think that there is a pretty strong argument for having (and knowing how to use) both :O

Oh and I would definitely agree with IO540 . . .

- most Narco stuff is crap

[LH2]

Steam instruments:

Plenty of failures, my first vacuum pump pack-up was early during my PPL. Had three and a half more since. On my last one a few weeks ago I flew across half of Europe and back on partial panel. Matter of fact, I don't think I've actually seen a working AH or DI in my last 50 hours.

On the planes I'm currently flying I had the only possible nav failure the other day: a leaking compass (therefore toppled rose). No AH, no DI, no VOR/ADF/GPS, not even a transponder installed, so not many chances of anything going wrong, other than the compass or the map flying out the window. :p

GPS:

Because of no moving parts, if the electronics are any good (and most of them are) they can withstand a surprising amount of abuse. I haven't personally seen aviation GPS failures as such. The ones I've seen in other environments where mostly due to sheer abuse or in some cases due to design choices which were not appropriate to the environment where the units where being used, mostly weak connectors, bad water/dustproofing, etc.

The most common navigation problems with GPS would appear to be people making wrong entries, database errors or omissions, or general user incompetence, sometimes compounded by bad user interface design. The system works, it just takes you to the wrong place.

So, different systems, different problems. Personally, since I don't fly commercially or for business purposes, I'm not too demanding on my nav requirements. As long as I end up more or less on the right country I'm pleased enough :E

[S-Works]

Perhaps wirth differentiating between a panel mount GPS, aviation handheld and the assorted collection of other stuff that people seem to bastardise for the job.

I have never had an IFR panel mount GPS fail in 3000hrs of using them. I have had a panel mount with a weak signal due to an antenna housing that had cracked and allowed water in over time. I have never had a failure on a aviation handheld from hardware problems and have been through 196,296 and now on 496. I have had signal loss on a couple of occasions when using the built in antenna when the panel mount 430 has still been perfect. I have not had a signal loss when the 496 is connected to the external active antenna.

I have had more steam bits of kit fail then I have fingers and toes to count. My ADF is a King ADF and every couple of years loses the plot and has to be reset. Main problems with the DME is moisture creeping into the display and the numbers not displaying. My HSI has failed a couple of times. The GNS430 is connected to both the HSI and a 106A indicator for redundancy. The Garmin indicator has never failed.

I have had numerous AI fail including one on a Seneca where the AP is connected to the AI and we were mid channel IMC and the AI toppled with the AP attempting to follow it.

I have had numerous vac pumps and alternators fail, all usually in IMC! I now have a redundant electric vac pump and NiCad battery pack to drive the avionics.

I would agree, most Narco kit is crap, although I have a couple of perfect examples over time that have been faultless. Alas the minority!

[IO540]

GPS mis-loading errors are easy to detect by using the moving map to zoom right out and display the whole route, before setting off.

A GPS without a moving map is OK for a door stop, nothing else.

Also a good idea to plan the route on VORs or NDBs, and tune in the navaid, for an enroute cross check.

That said, it is much harder to mis-program a GPS than to "mis-program" a VOR. On the latter, setting a track of 180 v 080 etc etc is easily done if in a hurry. In the goode olde days, pilots (including commercial ones) had little idea of where they were most of the time, other than when right on track to/from a navaid. We have an easy life nowadays.

I think basic failures will continue to dominate the avionics reliability picture. For example, in my TB20, most of the connectors around the avionics are high grade mil-spec jobs (the kind of thing you find throughout a King Air) and then they use Vauxhall Viva open plastic crap in the wings, going to the wingtip lights. All one can do with those (legally) is spray some ACF50 in them. A smarter plan would be to replace them with the good ones.

I am getting the whole aircraft corrosion-proofed soon - even though it is hangared.

[Cirrostratuss]

Although I consider GPS to be more useful than the steam stuff, I still rely more on the actual gauges than the GPS (if that makes sense). I've had two gps "failures" if you will. The first was caused by the GPS having a factory installed default of switching automatically off after 30 secs of no external power. During those 30 secs I was being a good pilot and keeping my head looking for traffic but when I checked the gps, it had turned itself off. That caused a major distraction on my part to get it back up and running and onto the right screen again (that setup has since been changed).

The second issue that I've had has been with poor gps signals. The only times that these have been an issue were while I was over the top with no ground visible below. The gps lost its signal for about 30 seconds.. then came back up for about a minute and then lost the signal again for 30 secs.

Both of these occurances have just reinforced my belief that the gps is a useful tool but not something you should rely solely on for navigation.

-Finn

[S-Works]

The gps lost its signal for about 30 seconds.. then came back up for about a minute and then lost the signal again for 30 secs.

I am assuming a handheld GPS not a panel mount? Which is why I said we had to differentiate. I have NEVER lost a signal on a panel mount IFR GPS even when I have had an antenna full of water.

If I am over the top of an overcast I would never consider a handheld as primary nav.

GPS is a PRIMARY tool for navigation. In the airways above FL95 is all we use for primary nav.

[IO540]

Cirrostratuss

The "faults" you list are not equipment failures.

The first is the result of not reading the user manual. And then flying with the unit for real before making sure it works as desired.

The second is the result of a poor signal - if using a handheld in a metal cockpit you should always use it with a window-mounted remote antenna. This is a common problem. A radio won't work very well in a metal box (with some holes in it) and a GPS is no different.

One could argue that there should be a ground course on GPS usage, and I would agree. But, having been to one such course some years ago and been the only one who turned up, I suspect there would be very few takers. The vast majority of GPS users are completely at home with gadgets (and have no problems working them out). The rest are probably too small a customer base, especially given there is no mandatory ground school in the basic PPL.

I think the OP was after views on equipment reliability, rather than the likelihood of mis-nav with a GPS versus other means. My view is that GPSs are on the whole far more reliable than other avionics, and also it is far harder to be misled when using them for navigation.

In 6.5 years of aircraft ownership, I have spent $1000 on a new LCD for my KLN94 GPS, and I am about to spend $3200 on an exchange KI-256 horizon (which costs $11,000 as a standalone buy - and these are prices direct from USA (http://www.seaerospace.com)). The overall pattern is that general avionics expenditure is an order of magnitude higher than GPS related stuff.

[PlasticPilot]

I got once a panel-mounted GSP failure - a GNS430 - due to a bad cabling. We could fly Geneva to Biggin-Hill IFR, using it, and a couple of days later, no signal. Hopefully, the leg home was VFR (no need for an certified GPS), and we had a couple of handheld devices on board.

Steam failures ? I got once a "heading bug" failure. As the HSI was turning, the bug was sometimes stuck, making its heading change, making the heading and interception modes of the autopilot unreliable.

[Cirrostratuss]

IO540

The "faults" you list are not equipment failures.

The first is the result of not reading the user manual. And then flying with the unit for real before making sure it works as desired.

The second is the result of a poor signal - if using a handheld in a metal cockpit you should always use it with a window-mounted remote antenna. This is a common problem. A radio won't work very well in a metal box (with some holes in it) and a GPS is no different.

I think the OP was after views on equipment reliability, rather than the likelihood of mis-nav with a GPS versus other means.And I agree with you completely. Thats why I specifically did not state that these were equipment failures but rather failures in general. I'm usually the first guy to scream RTFM but in this case the manual did not do a very good job of explaining that if a certain setting is in this config, then the unit will shut down by itself automatically. So for that reason I would classify it as a valid failure albeit not exactly related to equipment malfunction.

In the second case there were two handheld gps devices on opposite sides of the plane that lost the signal at the same exact time. Again, I'm not dumb enough to use a gps for primary navigation but for the uninitiated, this might still come as a surprise and potentially lead to problems if not using the old analogs for primary nav.

I do think the gps in whole are considerabily more reliable if used properly than any old steam gauge. And like I originally stated, much more useful in whole.

But thanks for the feedback, love to hear RTFM comments. :D

[IO540]

Again, I'm not dumb enough to use a gps for primary navigation

I have two questions.

1) Where is the legal definition (I mean the ANO, or the Civil Aviation Act) of "primary navigation"?

2) What would you use for primary navigation, and could you explain how this is better than other methods?

[bjornhall]

Ok, this time, inexperienced as I am, I don't agree at all... :)

GPS mis-loading errors are easy to detect by using the moving map to zoom right out and display the whole route, before setting off.

I prefer to check leg distances from the entered GPS route to leg distances from the plog. Easier to see "minor" but significant faults that way, IMHO...

A GPS without a moving map is OK for a door stop, nothing else.

Not at all! The moving map on something like a KLN89, or even a GNS430, I find rather useless... The KMD550 is the smallest unit I find really useful (I suppose a GNS530 is also large enough to be readable). On the other hand, I find the other functions on the GPS extremely useful, from the off-track indications when a route has been entered, to getting a quick bearing and distance to the airport when using direct-to. On the KLN89 I don't even bother using the moving map at all, yet I love that unit.

Actually, I would be perfectly happy with a GPS that featured only three functions:
1. A continuous readout of the current track
2. A continuous readout of the current groundspeed
3. A switch with which to turn the thing off in case of electrical problems

That is enough to take the crosswind problem out of simple map, compass and plog navigation. Even if I'm not using the GPS for anything else during a flight, I always use it for that: When turning to a new heading, first turn onto the planned magnetic heading from the plog; compare the GPS track to the magnetic track that I also have on the plog; adjust compass heading until GPS track matches plog track. Then it's back to looking out the window.

And I don't need a moving map to do that! :)


Also a good idea to plan the route on VORs or NDBs, and tune in the navaid, for an enroute cross check.

Can do that anyway; select "nearest -> VOR" on the GPS, tune in the VOR on the radio, and ensure the indications match (but I would agree this is more useful for a DME than a VOR, and even worse for an ADF). That way you can cross check indications whenever it is most convenient, without having to plan based on radio navaids.


That said, it is much harder to mis-program a GPS than to "mis-program" a VOR. On the latter, setting a track of 180 v 080 etc etc is easily done if in a hurry. In the goode olde days, pilots (including commercial ones) had little idea of where they were most of the time, other than when right on track to/from a navaid. We have an easy life nowadays.

If flying VFR, you'd often use waypoints that are not in the GPS database, wouldn't you? That means adding user waypoints manually, whether by place/bearing/distance or lat/long. Lots of digits to enter, in the usually awkward knob-twisting manner, and lots of possibilities for error.

[IO540]

The moving map on something like a KLN89, or even a GNS430, I find rather uselessThat I agree with. The KLN89/94 and GNS430 units I regard as nothing more than text-based route entry/management boxes. That job - styled I gather on the old FMSs - they do very well. My KLN94 does exactly what it says on the tin, and with total clarity and reliability. If it wasn't for that total crap called PRNAV :ugh: I would keep it for ever because it does everything required in the real world.

If flying VFR, you'd often use waypoints that are not in the GPS database, wouldn't you? No, never. Use VORs, NDBs, airway intersections. The only time I ever had to enter lat/long was for LEAX which in 2003 wasn't in the Jepp database. When one goes abroad, the last thing one wants to do, when asking for some CAS transit, is reading off some village name as the waypoint. Brit ATC don't like it much and foreign ATC even less.

[englishal]

A GPS without a moving map is OK for a door stop, nothing else.
Only is someone is a fcukwit and doesn't know how to use it;) I usually on a long cross country backup the 496 route onto my trusty eTrek - i download the route from my PC to the eTrek. Then if the 496 packs up I have some navigation. I also have a load of waypoints in my eTrek that I can use and worse case, I can manually enter a point.

The mean time between failures for conventional instrumentation is in the region of 800 hrs (FAA stats). For the Glass panels - and I suppose it goes for the GPS units like the 430/530's it is over 2000 hrs...