EFIS in extreme weather
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EFIS in extreme weather
Does anyone have experience operating EFIS equiped aircraft in extremely cold weather? We are going to be operating in an area where temperatures get down to -50 Farenheit for long periods of time. I've run steam gauge airplanes in this environment with no instrument failures but I'm concerned, mainly because of lack of knowledge, about how the EFIS screens will perform/last under these conditions.Thanks,Jim
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I highly recommend looking into the limits for your gear. Normally you'll find two sets, operational limits where it will actually work fine, and survivability limits where the equipment will survive but will need to be warmed up before it will power on ok.
Good luck with that though, with the thought of it I'm going to turn up my heating!
Good luck with that though, with the thought of it I'm going to turn up my heating!
The USAF don't have problems with the C17 or the Aussies with an A319 in Antartica so operating in those tempratures is OK. Now cold soak overnight and start up might be a different story.
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If the temp limits aren't in your FCOM, you should ask the manufacturer. IIRC, operating temps for TSO'd Arinc 700 avionics is -20 to +70 C. . EFIS is not TSO'd, however, but depends on TSO'd inputs.
Solid state components in avionics units are often operated very cold, to shake out the weak ones.
CRT EFIS generate quite a bit of heat, as does the backlighting on LCD EFIS, but cold starts should be avoided where practical. We used to cold soak intermittent avionics LRUs (Line Replaceable Units) in the shop, and then operate them as they thawed. Sometimes they would go wacky when passing through 32F, as ice inside them turned to dew. It would help to keep the humidity low on the fright deck and in the avionics compartment.
It would also be helpful to know what kind and age of fleet you have.
GB
Solid state components in avionics units are often operated very cold, to shake out the weak ones.
CRT EFIS generate quite a bit of heat, as does the backlighting on LCD EFIS, but cold starts should be avoided where practical. We used to cold soak intermittent avionics LRUs (Line Replaceable Units) in the shop, and then operate them as they thawed. Sometimes they would go wacky when passing through 32F, as ice inside them turned to dew. It would help to keep the humidity low on the fright deck and in the avionics compartment.
It would also be helpful to know what kind and age of fleet you have.
GB
Last edited by Graybeard; 5th Mar 2009 at 12:49. Reason: Clarification
What kind of A/C, and what electronics suite. Have used the AHRS down to -40 w/o problems, though the engines needed preheat to bring up oil temps. have also run frost fighters for 3 hrs to preheat hydraulics/gyros/engines etc....
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take at least 1 1/2 hours off your crew duty to account for the time it takes to carry out warm-ups on the jet.
Dont carry out any flight control checks until the hyd fluid has warmed up and the aircraft is de-iced - place the jet in EFCS and turn on the hyd pumps to allow fluid to circulate (procedure will be detailed in your FM).
You may pop a few cbs for the Hyd pumps as well when you start, one to watch for, as the fluid is cold and more viscous.
Get packs pumping out max heat as soon as you get to the jet and close up all doors to get it warmed up ASAP
Expect to have to reset the jet a couple of times or as a bare minimum, pull and reset system CBs as previously stated, electrics dont like extreme cold!
Oh, if you have LCD, it can take up to 10 minutes for the screens to warm up and display, turn them on and just let them warm up slowly. You may think they have failed, well they havent!
When you taxi off, check for wheel rotation - brakes may have froze on.
parking up the night before, check oxy system and especially toilets are purged of fluid or you can get split pipes. Not a pleasant thing to find.
Consider removing and storing batteries in a warm location so that you can get the damn apu running in the morning. Consider taking a charged spare battery or two.
Oh, Temperature Error correction (of course!)
Just my two penneth, most flight manuals have extensive sections covering the above, worth a solid study BEFORE you get there!
Oh, just thought of this one - DONT OPERATE OUTSIDE THE MIN TEMP LIMITS OF THE AIRCRAFT. Especially with EFCS.
Dont carry out any flight control checks until the hyd fluid has warmed up and the aircraft is de-iced - place the jet in EFCS and turn on the hyd pumps to allow fluid to circulate (procedure will be detailed in your FM).
You may pop a few cbs for the Hyd pumps as well when you start, one to watch for, as the fluid is cold and more viscous.
Get packs pumping out max heat as soon as you get to the jet and close up all doors to get it warmed up ASAP
Expect to have to reset the jet a couple of times or as a bare minimum, pull and reset system CBs as previously stated, electrics dont like extreme cold!
Oh, if you have LCD, it can take up to 10 minutes for the screens to warm up and display, turn them on and just let them warm up slowly. You may think they have failed, well they havent!
When you taxi off, check for wheel rotation - brakes may have froze on.
parking up the night before, check oxy system and especially toilets are purged of fluid or you can get split pipes. Not a pleasant thing to find.
Consider removing and storing batteries in a warm location so that you can get the damn apu running in the morning. Consider taking a charged spare battery or two.
Oh, Temperature Error correction (of course!)
Just my two penneth, most flight manuals have extensive sections covering the above, worth a solid study BEFORE you get there!
Oh, just thought of this one - DONT OPERATE OUTSIDE THE MIN TEMP LIMITS OF THE AIRCRAFT. Especially with EFCS.
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Other problems
I have operated the SF340 in several locations with these kinds of tempuratures. EFIS performed fine but there were plenty of other problem areas. If you're going to be there for a while, things WILL break. Good luck
Ace:
From what I have been able to determine, the low temperature limits arise due to the inability of an LCD type display screen to achieve the required levels of display brilliance at temperatures below -20°C. This temperature seems to be the "industry standard" low temperature operational limit for any avionics display system that uses an LCD type screen.
That doesn't mean that you can't read the screen at lower temperatures, it just means that the screen doesn't provide the levels of brightness and contrast needed to meet the certification specs when it is cold-soaked below that temperature. This is not a problem for aircraft that only use these type of displays for navigation purposes (e.g. Garmin 430, 530), but it can be a problem for aircraft that use these types of screens for display of engine instrument indications.
Fortunately, the screen is very thin (only a couple of millimetres), and it is only necessary to heat up the screen itself - not the whole box - to bring the brightness back up to spec. There are different ways of doing this. The most high-tech way is to specify a screen that has a metallic coating on it that can be electrically heated up - Barco, a major vendor of large format aircraft display screens, makes such a screen. A lower-tech way is to just aim a hairdryer at the screen from about 18 inches away and warm it up that way. An even lower tech way is to wrap a hot water bottle in a towel and place it over the face of the screen for a couple of minutes.
Once the screen temperature is at or above -20°C, you can start up the aircraft and use the aircraft heating system to finish warming the interior up. Once the flight compartment has warmed up a bit and you have confirmed that screen brightness is satisfactory, off you go.
To be honest, I could not imagine actually taking off with a flight compartment interior temperature below -20°C. I think that even in the worst possible environmental conditions (e.g. -50°C ambient), one would want to get the flight compartment air temperature up to at least 0 before takeoff.
Hope this helps.
From what I have been able to determine, the low temperature limits arise due to the inability of an LCD type display screen to achieve the required levels of display brilliance at temperatures below -20°C. This temperature seems to be the "industry standard" low temperature operational limit for any avionics display system that uses an LCD type screen.
That doesn't mean that you can't read the screen at lower temperatures, it just means that the screen doesn't provide the levels of brightness and contrast needed to meet the certification specs when it is cold-soaked below that temperature. This is not a problem for aircraft that only use these type of displays for navigation purposes (e.g. Garmin 430, 530), but it can be a problem for aircraft that use these types of screens for display of engine instrument indications.
Fortunately, the screen is very thin (only a couple of millimetres), and it is only necessary to heat up the screen itself - not the whole box - to bring the brightness back up to spec. There are different ways of doing this. The most high-tech way is to specify a screen that has a metallic coating on it that can be electrically heated up - Barco, a major vendor of large format aircraft display screens, makes such a screen. A lower-tech way is to just aim a hairdryer at the screen from about 18 inches away and warm it up that way. An even lower tech way is to wrap a hot water bottle in a towel and place it over the face of the screen for a couple of minutes.
Once the screen temperature is at or above -20°C, you can start up the aircraft and use the aircraft heating system to finish warming the interior up. Once the flight compartment has warmed up a bit and you have confirmed that screen brightness is satisfactory, off you go.
To be honest, I could not imagine actually taking off with a flight compartment interior temperature below -20°C. I think that even in the worst possible environmental conditions (e.g. -50°C ambient), one would want to get the flight compartment air temperature up to at least 0 before takeoff.
Hope this helps.
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Sorry if I wasn't clear. My concern was a cold soaked aircraft at 50 below then being brought up to operating temperature, over and over again. I just didn't know how the screens would react to this over time.
The ground crews will get the cockpit and engines warmed up before the flight crew arrives.
Jim
The ground crews will get the cockpit and engines warmed up before the flight crew arrives.
Jim
Obviously taking the temperature of anything down to -50°F and up to operating temperature multiple times is going to wear it out faster. Some avionics specify not only operating temperature but the temperature range the unit can be exposed to period. In this case it is usually because of worries about high temperatures though.
If you are pre heating the aircraft before starting the units that will reduce the wear and tear. Check your avionics manuals, if they do not say anything about non-operating temperatures I would say you are good to go.
If you are pre heating the aircraft before starting the units that will reduce the wear and tear. Check your avionics manuals, if they do not say anything about non-operating temperatures I would say you are good to go.
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The recent avionics certification standards (DO-160 in various versions) all specify a ground survival temperature of -55C. Your equipment will have been tested to that level, but will not necessarily have been subjected to multiple cycles that cold. At very low storage temperatures (usually below 40C) the fluid in LCD screens will partially freeze, just like water. It will thaw out again, and work normally, so there is no irreversible change in the fluid.
The problem is that when it freezes it makes crystals, again just like water. If you are unlucky, these crystals can damage the inside coating on the liquid crystal display, which manifests itself as "stuck" pixels on the screen when the display is back to working temperature again (usually stuck ON). These broken pixels are only a cosmetic defect until eventually after many freeze/thaw cycles they will become sufficiently irritating that you will want to replace the screen.
(I haven't had to replace an EFIS screen, but learned all this when working on a consumer electronics LCD screen product in a different life).
The problem is that when it freezes it makes crystals, again just like water. If you are unlucky, these crystals can damage the inside coating on the liquid crystal display, which manifests itself as "stuck" pixels on the screen when the display is back to working temperature again (usually stuck ON). These broken pixels are only a cosmetic defect until eventually after many freeze/thaw cycles they will become sufficiently irritating that you will want to replace the screen.
(I haven't had to replace an EFIS screen, but learned all this when working on a consumer electronics LCD screen product in a different life).
