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Multi-tasking: stumbling around on a hot day in a single-engine twin that should be able to fly just fine on one.

In a certain perverse way, it's interesting to contemplate the fate of the world's first multi-engine airplane pilot. The guy (or gal) who first took one of those early contraptions aloft likely had no real clue of what would happen if one of them failed. My dark side tends to smile, trying to conjure up the look on the pilot's face when the inevitable happened.

Nowadays, of course, flying a twin on a single engine is a well-understood challenge on which multiengine pilots regularly spend hours training and practicing. Every now and then, they have the misfortune of putting those skills to actual use, hopefully at an altitude and speed making engine failure a non-issue: Just motor over to the nearest suitable airport and land. Of course, it's not that simple, but it gets even more complicated when an engine fails while the average light piston twin is still low and slow, like on a takeoff. That's where much of the training is focused and where much of the danger exists. Still, there is a set of procedures and a decision-making process the pilot can use to get the airplane safely back on the ground.

When I trained for my multi-engine rating in a non-turbocharged Seneca, my instructor and I thoroughly explored the airplane's low-speed capabilities. I came away with a healthy respect for the airplane's lackluster performance on one engine, more than willing to sacrifice the airframe by rolling off the far end of the runway into the weeds instead of trying to stagger around the pattern to return after an engine failure. We also made each takeoff an exercise in extracting all the performance the airplane could offer until we were at pattern altitude.

Fortunately, I've never had to face the challenge of losing one of a twin's engines during a takeoff. But one thing I picked up from that training--and it applies also to flying a single, a sailplane, a helicopter or a jet transport--is that I want to contact the ground under control and at the lowest possible speed. In a light twin, meeting that objective may require closing both throttles, establishing a safe glide speed and putting down the airplane on the most suitable nearby terrain.

BACKGROUND

On July 24, 2005, at 1752 Central time, a Cessna 310Q was destroyed when it collided with terrain shortly after takeoff from the Ada Municipal Airport (ADH) near Ada, Okla. The Airline Transport pilot, the two passengers and a dog were fatally injured. Visual conditions prevailed.

A security camera shows the airplane in its initial takeoff climb from Runway 17 at between 1751:25 and 1751:30. The airplane's altitude appeared to be just below the tops of trees located east of the runway. During this time, a sudden burst of white-colored smoke was observed coming from behind the right engine. The airplane is then observed entering a right turn toward the west with the landing gear extended.

Between 1751:34 to 1751:42, another camera captured the airplane as it flew toward the west at an altitude just above the airport hangars with its landing gear retracted. From 1751:52 through 1752:47, a third camera recorded the airplane as it flew toward a tree line west of the airport and disappeared behind the trees. Shortly, a pillar of dark smoke began appeared above the tree line where the 310 was last observed.

According to a witness who did not hear the airplane until it was almost right over him, the 310 was "extremely low" and in a shallow right turn to the north. Shortly, the airplane's nose dropped and it rapidly descended, struck the ground and cartwheeled. The witness added he did not see any fire or smoke trailing the airplane but did hear a "miss in the engine." He added that the airplane did not sound as loud as other airplanes do when they depart and believed "it was not making the power it needed to maintain altitude."

On November 18, 2004, the airplane's right engine was replaced with a factory-new one. Prior to departure, 20 gallons fuel were added to the tanks, bringing the fuel load to approximately 1/2-to-3/4-full. Reported weather at 1752 included wind from 160 degrees at 10 knots gusting to 18 knots and a temperature of 97 degrees F. The calculated density altitude was 3700 feet.

INVESTIGATION

The right engine's failure was linked to a fractured crankshaft gear, which lost several teeth. Improper heat-treating of the gear was found, but could not conclusively be blamed on the gear's failure. The right propeller was feathered at the time of impact. Blades from the left propeller exhibited minimal damage, consistent with impact at low power.

The NTSB and Teledyne Continental Motors (TCM) closely examined the failed crankshaft gear. According to the NTSB, "it was evident that the microstructure of the gear was inadequate and more research into the manufacturing process was required." As part of its investigation, TCM manufactured several other gears at different hardnesses and conducted failure testing, attempting to reproduce the failure. Even though some of the hardness levels were well below TCM standards, they were unable to produce a similar failure. The cause of the gear teeth failure could not be determined.

Published performance data revealed that the airplane would need approximately 3400 feet to clear a 50-foot obstacle with one engine operating. The single-engine climb performance would have been approximately 250 fpm.

PROBABLE CAUSE

The NTSB determined the probable cause(s) of this accident to include: "The loss of engine power as a result of a fatigue fracture in one of the crankshaft gear teeth for undetermined reasons. Also causal was the pilot's failure to maintain control of the twin-engine airplane after the power loss, which resulted in an inadvertent stall and subsequent collision with terrain."

The NTSB's focus on the failed crankshaft gear is laudatory, but really wasn't the primary factor. Instead of being "also causal," the pilot's "failure to maintain control" of the 310 should have been more closely examined. To be sure, the pilot was handed an engine failure at the worst possible time but, given the conditions and predicted airplane performance, along with his ATP training, he should have been able to pull this off.

We don't know if he was trying to return to land, trying to execute an off-airport landing or just stumbling around: The left engine's low power output at impact is inconclusive. Based on the evidence, however, along with the airplane's low altitude, it's not at all clear the pilot was trying to extract the airplane's maximum single-engine performance. For now, we'll go with stumbling around.

AIRCRAFT PROFILE: CESSNA 310Q

[ILLUSTRATION OMITTED]

ENGINES: CONTINENTAL IO-470-VO

EMPTY WEIGHT: 3214 lbs.

MAX GROSS WEIGHT: 5300 lbs.

TYPICAL CRUISE SPEED: 192 knots

STANDARD FUEL CAPACITY: 102 gal.

SERVICE CEILING: 19,500 ft.

RANGE: 680 nm

Vso: 63 knots

The Lazarus Maneuver

Safely flying a conventional twin on one engine requires two things: understanding the aerodynamics and good training. One of the objectives is to properly establish a zero-sideslip attitude, which maximizes the airplane's performance on one engine. According to the FAA's Airplane Flying Handbook, FAA-H-8083-3A, here's why: "With a single-engine airplane or a multiengine airplane with both engines operative, sideslip is eliminated when the ball of the turn and bank instrument is centered ... and the airplane is presenting its smallest possible profile to the relative wind. As a result, drag is at its minimum.... The AFM/POH performance charts for single-engine flight were determined at zero sideslip. If this performance is even to be approximated, the zero sideslip technique must be utilized."

[ILLUSTRATION OMITTED]

In essence, the zero-sideslip maneuver translates into "raising the dead" engine's wing slightly to offset the asymmetric thrust condition. By turning into the failed right engine--the record is clear the 310 was in a shallow right turn throughout the accident sequence--the accident aircraft's pilot was never going to obtain book single-engine performance.

[ILLUSTRATION OMITTED]
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Title Annotation:ACCIDENT PROBE
Author:Burnside, Joseph E.
Publication:Aviation Safety
Geographic Code:1USA
Date:Jul 1, 2007
Words:1326
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