Bleed Air Fail Light-B200

[FOD_Vacuum]

Hey quick question for maintenance about the Super King Air 200: Our R/H Bleed Air Fail light came on during a dark, cold (-42) morning climb up into the flight levels (came on thru FL180). Woke us up pretty good, ran memory items, shut off Bleed Air valve INST and ENVIRmnt off, watched instruments and followed up with checklist. One bleed Air couldn't keep up with our selected cabin px altitude, and ended up 2000ft higher than selected and we leveled off slightly lower (FL210) for the rest of the flight.

After we turned off the bleed air switch, the light went out again. Should it not have stayed on if the line ruptured and tripped the light on? The same happened a couple of days later with the same company aircraft. Any ideas what couldn't have triggered the light to come on? The coldness??? Doubt it..

[nine sixteenths]

There are two little pressure switches under the floorboards below the co-pilot's seat, one for each side. These are what turns the lights on and off. Its very possible one of those switches is on it's way out. That's not an uncommon thing to see fail, which can cause the lights to go on and off somewhat randomly. If the plane was cold soaked, its possible there was a little frozen water in one, but not terribly likely as they are mounted so any liquid would drain down out of them.

Both switches get their air from a common, regulated manifold, located in the center aisle, but each side has its own EVA tubing (light plastic tube) that follows its own path through the aircraft. These lines follow your bleed air lines through the cabin, out under the center section leading edge, in your wheel well, in the sides of the nacelles, (possibly other areas as well, I can't recall off the top of my head), then the EVA tubing for both sides runs side by side up the ductwork under the right side of the cabin floor, until they terminate at the switches under the seat.

Assuming you don't have a major bleed air line break, when an EVA tube ruptures its usually a very small hole (pinhole size, and with the edges blown outwards). The pressure in that line decreases to 1-2 psi and the switch for that side is activated. As there is a lot of volume of air available to the system at that manifold, the other line stays pressurized, so that switch does not go out.

In your situation, since the light went out again, I would guess that you don't have an EVA tubing failure, but you do have either an indication problem in your panel (not really likely, but possible), or one of those little switches is failing. Again, they are just cheap little pressure switches, so its not really a surprise when they do fail.

Hope that helps clear things up for you,

9/16

[plhought]

The above is all good advice.

If you really want to get into it blow out the EVA lines w/ some air (nitrogen preferred) and clear out the muck/moisture. At the same time one can test the pressure switches. Be responsible though. Don't throw 90 PSI through the thing. Usually this kind of fault develops early in the icing/cold season.

The bleed system on the KA is really reliable and barring a brutal leak (which has ruptured the EVA tubing) or a complete flow pack failure. I'd say 75% of the time the BL FAIL indications are down to nuisance leaks (the line in some models is plugged with a rivet/screw...) or a junky pressure switch.

Don't be afraid to take a good wiff of smell in the Cabin if you suspect something a little more serious. If there's a leak in in the pressure vessel it'll be pretty obvious.

But what ya did is all correct and since the indication went out 9/16ths is pretty much spot on. On newer KA's and one-nine-hondos the press. switches are located a bit differently back behind the spar.

[Pat Richard]

If you selected a flowpack and it wouldnt maintain selected altitude, the pack is probably faulty. Maintenance can test for this. The most common area I ve seen that line punctured is the center spar area. It generally gets stomped on when the floorboards are up.

[GyvAir]

The most common area I ve seen that line punctured is the center spar area. It generally gets stomped on when the floorboards are up.

Also suspect, is anywhere someone has recently been up to their armpit trying to work on some other under-floor component, not realizing that they've been stretching the tube too close to the bleed air lines.

If you selected a flowpack and it wouldnt maintain selected altitude, the pack is probably faulty.

Very possible, but given the age and mileage on much of the King Air fleet, I wouldn't discount the cumulative effect of 1000 little (or not so little) pressurization leaks.

[Pat Richard]

Gyvair - only reason I suggested the pack is weak is I assume the other pack would maintain cabin alt. + regulated 18 psi bleed air warning tube pressure.
Cumulative mass leakage is very possible. I had exactly that issue on 3 different airframes. Good indicator was changing flowpacks frequently, although a shitty overhaul facility causes that too, lol.

[FOD_Vacuum]

Thanks for the reply's guys-its hard to visualize the different parts and components as I have not been shown any of them underneath floorboards etc. I just fly the planes and have OK knowledge of the system, but not the same as maintenance personnel obviously. Il look into it with all the feedback's taken into mind!

[rigpiggy]

the EVA tubing will also get brittle with age, last time this happened to me tube was cracked almost all the way around at the pressure switch, it would move just enough in turbulence to release the pressure, set off the light then go out

[ramaniv302]

Hey guys, kinda similar problem we are experiencing lately but only during start up and not during flight. Let me explain you in detail about the situation from the start. Both the bleed air valve switches are in "ENVIR OFF" position. We start the RH engine, we notice "R BL FAIL" warning light extinguishes while the "L BL FAIL" warning light is still illuminated for a long time (more than 10 secs +). Sometimes we start the LH engine, and the "L BL FAIL" warning light extinguishes.

Now when the bleed air valve switches are moved to "PNEU & ENVIR OFF" position, both the left and right bleed air fail warning lights should illuminate immediately. But only "R BL FAIL" warning light illuminates immediately, whereas "L BL FAIL" warning light illuminates approximately 10 secs later.

Now when we again move the bleed air valve switches to "ENVIR OFF" position, both the warning lights extinguish immediately as normal and we do not notice any trouble after this point.

There is no time difference limit mentioned in the AMM. Is the time delay permissible? Can this be even termed as a problem? What could be possible cause of such a time delay which we have experienced only during start up? And basically we are from India, so its warm and humid out here (average daily humidity for the month of Jan was 61%).

Thanks.

[GyvAir]

Same as 9/16 said in his earlier post: I would suspect the LH pressure switch itself to be starting to fail, if it's slow to both actuate and de-actuate. Relatively easy item to test/swap and rule out at least.

[PostmasterGeneral]

If the lights take a while to come on after the switches are moved to off, keep your eyes on the pneumatic pressure gauge and with the valves closed, blow the boots. The lights should both then come on. It's possible there it just some residual pressure making its way past the shutoff valves into the system.

[Meddler]

I'd say being able to stay at fl210 on one flow pack is pretty good, considering the age and leaky nature of some 200s.