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A small problem gets big

The perils of brushing off minor maintenance

The odor coming from the overhead vent was faint but persistent. Cruising in smooth air in the high flight levels with engine and pressurization systems seemingly normal, I opened the Cessna Citation’s abnormal checklist but couldn’t find anything that addressed this situation.
Photography by Mike Fizer
Photography by Mike Fizer

Smoke in the cockpit would be an obvious emergency that would demand donning an oxygen mask and landing as soon as possible—but the barely perceptible odor didn’t rise to that level. I chalked it up to residue from a recent cockpit cleaning and then got busy with other tasks.

But the odor didn’t go away on subsequent flights. It remained. The maintenance staff attributed the smell to residue from the aircraft cleaning, even though it didn’t fade as expected over time.

Besides, other issues with this airplane were more pressing. Its avionics suite was bedeviled by intermittent gremlins; its left engine consumed noticeably more oil than the right; and the maintenance staff was focused on resolving some paperwork oversights inherited from a former manager. A minor odor in the cockpit on a low-time airplane remained far down the priority list—until a cold-weather takeoff in the Midwest moved it straight to the top.

It was 11 degrees Fahrenheit as we boarded the Citation for a two-hour flight to the East Coast. The aircraft owner and one of his business associates were the only passengers, and we were looking forward to catching a booming tailwind that would increase our groundspeed by 100 knots or more at altitude.

“Give us some heat back here as quick as you can,” the owner called out as I started the engines. “It’s chilly.”

I took off my gloves to use the G3000 touchscreen controllers and programmed the bleed air system to provide maximum warmth to the cabin. It was the first time I’d done that in this airplane since our previous trips had been to warm weather destinations where air conditioning—not heat—was the priority.

Takeoff was normal, and the airplane climbed energetically in the frigid morning air. But that nagging cockpit odor was back, and this time it was stronger than ever.

Then I looked at the vent on the right side of the cockpit and saw what looked like fog streaming in through the side vent. I quickly turned off the heat, and that stopped the fog machine. The smell wasn’t acrid. It wasn’t smoke from an engine or electrical fire. But I couldn’t identify it either. And the fact that it disappeared as soon as the heater went off seemed like a pretty strong clue about its source.

I opened the overhead vents and the air soon cleared. Then I resumed the climb with engine and pressurization indications normal. As long as I left the air distribution system in its automatic setting with manual heat off, things seemed fine, so it stayed that way for the duration of the flight.

After landing, I asked the passengers whether they’d noticed anything unusual during the climb, and they both said there had been a strange smell and a fine mist inside the cabin.

When I told the mechanic about the anomaly, he immediately connected two bits of information that I hadn’t considered related: the faint odor and relatively high oil consumption. “Now we know where the oil from the left engine is leaking,” the mechanic said. “Somehow, it’s finding its way into the bleed air system.”

The larger lesson here is to address seemingly minor maintenance discrepancies before they become major. The cockpit odor had been a trifling annoyance for weeks until it became an acute problem. And a timely engine inspection might have diagnosed the leaky seal that caused the left engine to use more oil than its twin. The repair, after all, was a relatively minor gasket replacement.

Maintenance can be costly and time consuming, and there’s almost never a convenient time for it. It’s tempting to defer small items so they can be compiled and addressed all at once. The manager of this Citation, for example, was already planning to have the engines inspected during its next scheduled visit to a service center a few weeks later. No one wants to “fix things that ain’t broke,” and the efficacy of making repairs “on condition” rather than hourly schedules has long been proven. But once an airplane tells us there’s a problem—even if the evidence is as subtle as a faint odor—the old saw about fixing things that ain’t broke no longer applies. It’s time to act.

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Dave Hirschman

Dave Hirschman

AOPA Pilot Editor at Large
AOPA Pilot Editor at Large Dave Hirschman joined AOPA in 2008. He has an airline transport pilot certificate and instrument and multiengine flight instructor certificates. Dave flies vintage, historical, and Experimental airplanes and specializes in tailwheel and aerobatic instruction.

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