AOPA Pilot Magazine - July 2023 - 28

SAFETY SPOTLIGHT
No smoking gun
A stealthy burglar stealing your power
BY RICHARD MCSPADDEN / Senior Vice President, AOPA
Air Safety Institute / AOPA Foundation Legacy Society member
VAPOR LOCK. While airborne. I didn't know that was a thing until
recently while flying my colleague's Socata TB30 Epsilon. The
Epsilon had flown twice that warm spring day with no issues. I
fueled it up, then hopped in the backseat to give an Epsilon checkout
and spin instruction to a newly minted CFI.
We cranked normally, then started a long taxi. We were number
seven for takeoff at Frederick (FDK). We leaned the Epsilon during
ground operations and occasionally bumped power and tickled
the boost pump to keep the engine idling on a hot, stagnant ramp.
We turned the boost pump on-normal Epsilon takeoff
procedure-and the front-seater went full throttle for a takeoff
with normal engine readings. He cleaned up gear and flaps, turned
the boost pump off at about 1,000 feet, and began a climbing turn
for departure. All seemed nomal, albeit with warm cylinder head
temperatures in the 400- to 418-degree range. A CHT of 420
degrees is higher than preferred for cruise, but not unheard of
for big Lycomings on a warm-day climb, so we retarded power
to slightly below normal climb setting, checked the mixture rich,
and continued a 120-knot cruise climb on our way to 6,000 feet.
A few minutes later, still climbing, the front-seater reported
engine oil temperature rising rapidly and approaching redline. I
smelled burning oil. I took the airplane, lowered pitch, powered
back, and the engine stumbled-hard. I powered back up, but the
engine kept stumbling, so I turned on the boost pump and checked
mixture, still full rich. The engine responded better, but still
wouldn't produce full power. Oil temperature hovered just below
the redline. We powered back, turned back to the field, and began
pitch to best glide. The engine still wouldn't make enough power
for level flight. In the descent with power back, the oil temperature
began dropping. One problem neutralized.
We switched back to tower, declared an emergency, and
reported our position, eight miles to the northeast. If the engine
held, we seemed to have enough altitude and power to make it
back to Frederick. We scouted farm fields and a couple of grass
strips along our path, good options for a potential off-airport
landing if the engine degraded further.
What could be the problem? We tried isolating magnetos to no
effect and switched fuel tanks, also to no effect. We turned the boost
pump off and the engine lost more power and seemed likely to quit.
OK, boost pump needed to keep the engine running. Even then it only
28
AOPA PILOT / July 2023
resulted in rough partial power. We flew a high straight in, pointing
a third of the way down the runway and delayed gear extension until
just before the threshold, then dropped in a steep descent to land a
couple thousand feet long. On the ground, no difference from the
air, the engine would quit without the boost pump.
We shut down and an A&P/IA investigated. He checked
pressure from the engine-driven fuel pump; flow through the
fuel lines; and fuel sump samples. No smoking gun. Later he
cranked the engine, idled it, ran it up, then powered back to idle,
but could not duplicate the problem. The dreaded CND: could not
duplicate-annoying to maintenance, hated by pilots.
Another inspection and analysis of engine data downloaded
from the Garmin G3X clearly indicated where the problem had
occurred in the flight profile. Several phone calls with Epsilon
club members and engine experts left the general consensus that
it must have been an airborne vapor lock, a burglar that will steal
thrust and leave no trace. A similar event happened another time,
in similar conditions with an Epsilon. They never found evidence
of a problem, and it's never occurred again. Other airborne vapor
lock stories began to emerge from interested maintenance
professionals now engaged in analyzing my CND event.
The clearing procedure for airborne vapor lock is boost pump
on, full rich, full power, pitch down if able to help cooling. But in
our case, that didn't work. At least I don't think it did. I started
second-guessing my throttle position after I powered back to
control the oil temperature. I was worried about protecting the
engine, so maybe I didn't ever go back to full throttle once I knew
partial power would make the field. I can't be certain.
Several of us with a lot of GA time learned of a new bogey that
day: airborne vapor locks. Fortunately they're rare and isolated to
hot days where the engine gets warm on ground operations and
continues warmer than average operations airborne.
Go fly. Think hard about engine temperature management
if you find you need higher power and the boost pump to keep
your engine idling on the ground.
Your engine might be warning
you of a stealthy burglar
casing the joint.
richard.mcspadden@aopa.org
SpadMcSpadden
PropBlast
RICHARD MCSPADDEN
is a CFII, MEI, SES, MES
rated commercial pilot
with a Citation single pilot
type rating.
AOPA Pilot Magazine - July 2023

Table of Contents for the Digital Edition of AOPA Pilot Magazine - July 2023
