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Singles vs. Twins: A Case Study

It’s hard to argue the 'single vs. twin' debate ... especially with someone who had just put a single-engine airplane down off-airport following a catastrophic engine failure.  This endless debate has no statistically provable answer (many twin-engine failures end with a successful single-engine landing and no accident report, and even some in-flight engine failures in single-engine aircraft end up with a glide to a runway and don’t land in the record books).  I do have some information, however, that helps draw some conclusions about the relative safety of single- and twin-engine airplanes.

It’s hard to argue the 'single vs. twin' debate ... especially with someone who had just put a single-engine airplane down off-airport following a catastrophic engine failure.  This endless debate has no statistically provable answer (many twin-engine failures end with a successful single-engine landing and no accident report, and even some in-flight engine failures in single-engine aircraft end up with a glide to a runway and don’t land in the record books).  I do have some information, however, that helps draw some conclusions about the relative safety of single- and twin-engine airplanes.

I track mishap reports involving piston-powered Beech airplanes for a number of pilot training organizations and individual subscribers.  Here’s the information I have on these airplanes for calendar year 2003:

ENGINE FAILURES
Total reported: 43
Single-engine: 30
Multi-engine: 13

BY SCENARIO

ENGINE FAILURE IN FLIGHT
Total reported: 18
Single-engine: 15
Multi-engine: 3

ENGINE FAILURE ON TAKEOFF
Total reported: 9
Single-engine: 8
Multi-engine: 1

ENGINE FAILURE ON APPROACH/LANDING
Total reported: 5
Single-engine: 1
Multi-engine: 4

FUEL STARVATION/EXHAUSTION
Total reported: 7
Single-engine: 6
Multi-engine: 1

ENGINE FIRE IN FLIGHT
Total reported: 4
Single-engine: 0
Multi-engine: 4

DEFINING THE STATS

Of the 43 reported engine failures in Beech piston airplanes in 2003, 70% were in single-engine airplanes while 30% were in twins. Inside Information: Considering the relative number of piston Beechcraft produced, singles vs. twins, a higher-than-expected percentage of twin-engine Beechcraft were involved in engine-related accidents.  This suggests (at least on the surface) that the second engine does not reduce the rate of engine-related mishaps ... and may actually make them more likely. However, this might be slightly offset by the typically higher utilization rate of twins vs. singles.

Twice as Likely to Fail?
There's a strong case to be made that the twin-engine pilot is twice as likely to experience an engine failure as his or her single-engine counterpart.  Pilots as far back as Charles Lindbergh used this logic to explain their preference for single-engine airplanes.

If this thinking is true (and it is logical), than the above analysis suggests that a little more than half of all multi-engine power plant failures result in a mishap. Hence, although having the second engine is not a panacea for engine-related accidents, the possibility exists that something can make up for the increased likelihood of an engine-related accident in twins, allowing the pilot to realize the safety benefit of the second engine.  That “something” is improved pilot training and proficiency. Next time, we'll take a look at some of the very specific differences in the pilots and the scenarios they face when engines fail in light twins and light singles.

 

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About This Author:
Tom Turner is a widely published author and regular forum speaker at EAA's Oshkosh/Airventure and American Bonanza Society. Tom holds an M.S. in Aviation Safety with an emphasis on pilot training methods and human factors. He has worked as lead instructor at FlightSafety International, developed and conducted flight test profiles for modified aircraft and authored three books including: Cockpit Resource Management: The Private Pilot's Guide and Instrument Flying Handbook (both from McGraw-Hill). His flight experience currently spans 3000 hours with approximately 1800 logged as an instructor. Tom's certificate currently shows ATP MEL with Commercial/Instrument privileges in SEL airplanes.
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