Plane & Pilot – September 2019

16 SEPTEMBER 2019 ÇPlane&Pilot

PIPER PA28

Bonifay, FL/Injuries: 1 Fatal

The owner of the airplane experienced a partial loss

of engine power during takeoff following a touchand-

go landing, but was able to complete a 180° turn and

land safely back on the runway. During a post-landing

engine run-up, the owner was unable to duplicate the

problem, so he taxied to his hangar and reported the

problem to his mechanic. The mechanic, a commercial

pilot, subsequently boarded the airplane, performed

an engine run-up, which seemed normal, and elected

to fly the airplane around the airport traffic pattern.

A witness, who heard and saw the airplane on final

approach, stated that the engine was making “small

explosions” or “backfire”-like sounds. The airplane

subsequently collided with a tree before it impacted the

ground and a fence short of the 4000-foot-long runway

and was consumed by a postcrash fire.

Examination of the airplane revealed that the No. 4

cylinder exhaust valve was stuck in the “open” position

due to excessive deposits from the combustion process.

It is likely that the stuck exhaust valve resulted in the

partial loss of engine power. Maintenance records

revealed that the engine had not been inspected in

accordance with a manufacturer service bulletin regard-

ing stuck valves. Had the service bulletin been complied

with, it is possible that the accident may have been

prevented. Despite the partial loss of engine power

that occurred during the previous flight, the pilot flew a

traffic pattern that resulted in the airplane descending

into trees about 1/4 mile before the runway threshold

after the airplane experienced a partial loss of engine

power during the accident flight.

The pilot was diabetic, and although his blood glu-

cose was likely not very elevated at the time he died, it

was somewhat elevated on average over the preceding

few weeks. Elevated blood glucose can cause blurred

vision and subjective sensation of fatigue, as well as

increased thirst and urination. Unless life-threatening, it

does not directly impair decision-making or judgment;

thus it is unlikely that the pilot’s diabetes contributed

to the circumstances of this accident.

PROBABLE CAUSE(S): A partial loss of engine

power due to a stuck exhaust valve. Contributing to the

accident was the pilot’s decision to operate an airplane

with a known mechanical deficiency and his failure

to fly an appropriate traffic pattern that would have

allowed the airplane to reach the runway.

MOONEY M20E

Skyforest, California/Injuries: 1 Serious,

1 Minor, 2 Uninjured

The private pilot reported that, a few minutes after

departure for a cross-country flight and as the airplane

neared the top of a ridgeline, it encountered a down-

draft, aerodynamically stalled, and then impacted

terrain. One of the passengers reported hearing an

aural tone, which was consistent with the stall warning

horn, for several seconds before impact.

Weight and balance calculations determined that

the airplane was loaded near its maximum gross weight

and had exceeded the forward center of gravity limit,

which would have increased the airplane’s stall speed

during the accident flight. The calculated density

altitude was about 6,550 ft, which likely reduced the

available power and affected the climb rate.

A video of the final moments of the accident flight

showed the airplane about 25 ft above ground level

when the airplane entered a high pitch attitude, fol-

lowed immediately by a rapid descent, consistent

with an aerodynamic stall. According to the pilot,

the airplane was about 1,000 ft above terrain when it

stalled; however, given the location of the camera and

the pitch attitude that was observed, it is likely that

the airplane was within about 50 ft of terrain as the

airplane crested the ridgeline. The pilot should not have

attempted to cross the ridgeline at such a low altitude;

a higher altitude would have provided a clearance zone

to avoid turbulence and downdrafts. The pilot’s failure

to cross at a higher altitude resulted in the airplane’s

encounter with a downdraft with insufficient altitude

to recover from the stall.

The pilot reported that there was no evidence of

any preaccident mechanical malfunctions or failures

with the airplane that would have precluded nor-

mal operation.

PROBABLE CAUSE(S): The pilot’s failure to

establish the proper airspeed after departure and to

maintain adequate clearance from a ridgeline in high-

density and downdraft conditions and his subsequent

exceedance of the airplane’s critical angle of attack,

which resulted in an aerodynamic stall with insuf-

ficient altitude to recover. Contributing to the accident

was the pilot’s inadequate preflight weight and bal-

ance calculations, which failed to take into account

the gross weight, high-altitude conditions, and center

of gravity limit.

NOTE: The reports republished here are from the NTSB and are printed verbatim and in their complete form.