CRJ: "fuel smell" when APU started

[Typhoon1244]

Our procedures call for starting the APU when descending through 10,000 for landing. Yesterday, right after the APU stabilized--but before we transferred the packs to the APU bleed--we got an overwhelming Jet-A odor in the cockpit and the cabin. We shut the thing down right away and pressed on through the approach bleeding the engines to the packs. No big deal...just like having a deferred APU.

This is apparently not an uncommon problem on the CRJ, but I don't have much info. about it. Anybody have any leads on what's causing the strong fuel odor after APU start?

 

[skyboat]

Fuel leak in aft equipment bay.At least this it was the several times it happened to me. Each time it has happened, jet fuel was dripping out of the aft equipment bay on postflight. One time the APU shut itself down because it wasn't getting any fuel.

Another more common problem is oil seals on the APU. If you ever smell an oily smell coming out of the vents, stand by for an APU autoshutdown as it is most likely spewing oil all over the aft equipment bay. The big danger with this is the packs are spewing out very highly atomized turbine oil into the cabin. You then breathe this and it gets ionto your lungs, and then your bloodstream because it is so highly atomized. Not a good thing.

 

[cl-65link]

Did it start on the first attempt? In the CRJ, if you wait to long to hit the start switch, after pressing the power/fuel switch, the logic in the ECU will prevent a start(in the air). I had a hamfisted FO do this to me once. This is the only time I have ever had such a problem with the APU and Jet-A fumes.

 

[CRJ_Driver]

I've never experienced any Jet A fuel smell associated with starting the APU nor any Oil smells that would raise an eyebrow.

As far as the APU start sequence being interupted...yes...but waiting a few minutes will solve it...or a breaker behind the Capt!

 

[jborsdrf]

Twist and shout

Funny you guys should mention this I notice in the ERJ we often smell Jet A right after starting the APU on decent. It always goes away after a few minutes but it is often a strong oder.

On a somewhat related note do you CRJ drivers ever have to retrim the rudder after turning on or off the APU. The ERJ requires a touch a trim, most pilots attribute this to twisting of the fuselage due to some sort of gyro effect. Others seem to think this is due apu exhaust, but it goes straight out the back so I don't really buy that.

 

[flywithastick]

Re: Twist and shout

twisting of the fuselage due to some sort of gyro effect.

compare the mass of the AC versus the mass of the apu wheel... my money'd be on the exhaust, no question.

Others seem to think this is due apu exhaust, but it goes straight out the back so I don't really buy that.

Even though the exhaust duct faces the rear, you sure it doesn't flow to one side?

Back to the fuel smell... I'd fall back on basic troubleshooting. You ever smelled it before? What configuration? Anything different in this situation? If you've flown in this configuration plenty of times, everything indicates operating normally, then I'd say something's broke/leaking.

If something fails, something has changed. With planes and industrial machinery, they almost always "tell you" before they fail. Let us know if you find anything out.

 

[XLR8]

I've had that fuel smell in the CRJ before too. I had it when after attempting to start the APU and it didn't, deselected the start/stop switch and the pwr fuel switch....tried it again a couple minutes later.....it started and transfered the bleeds and then got the smell.

I'm assuming it was just some leftover fuel.....I think when that happens it's better to to start it......let it run for a while and then transfer the bleeds, just to make sure all the smells get out of there.