Out Of Range

No airplane is perfect for every mission. Designers make compromises in the hope of producing an airplane that will find enough buyers to be a marketing success. But buyers have proven they sometimes want what manufacturers won’t provide, so we have a lively market in aftermarket mods. One popular mod is for more powerful engines in airframes like the Cessna 172. The results include better climb, a little faster cruise and, unfortunately, higher fuel burn. All aftermarket modifications to an airplane come with drawbacks. They can be as simple as a bit of added weight and a logbook entry or complicated enough to require a lengthy supplement to the paperwork. The more we alter the airplane’s original performance, the more we need to understand the mod’s impact on the airplane’s other characteristics.

Joseph E. (Jeb) Burnside

Friday, August 24, 2012 at 12:00 AM ET

Verified

Key Takeaways:

Aftermarket engine modifications, while improving aircraft performance, significantly increase fuel consumption, a critical factor for flight planning.
A fatal Cessna 172 crash was attributed to fuel exhaustion, as pilots failed to account for the higher fuel burn rate of an aftermarket engine modification during flight planning and in-flight fuel management.
It is the pilot's responsibility to utilize accurate, up-to-date aircraft data, particularly for modified aircraft, to ensure sufficient fuel reserves for safe flight operations.

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All aftermarket modifications to an airplane come with drawbacks. They can be as simple as a bit of added weight and a logbook entry or complicated enough to require a lengthy supplement to the paperwork. The more we alter the airplane’s original performance, the more we need to understand the mod’s impact on the airplane’s other characteristics. When we add more power to an airplane, for example, we also burn more fuel. What can happen to an airplane’s “book” fuel burn after a very modest power boost is this month’s lesson.