Expert: D. Norkus - 1/15/2012

Question
Hello: While reading about a recent crash landing of a Piper PA-31 Navajo on approach to North Spirit Lake, Ont,resulting in 4 fatalities from a post crash fire,it occurred to me that improved fuel tanks might have saved lives.Is it practical to retrofit small commercial aircraft with crash resistant fuel tanks? I was thinking along the lines of Explosion Suppressant Foam filled tanks,like the ones manufactured by Crest Foam Industries ( http://www.crestfoam.com/intro.html). I can imagine that economics enters into the equation,especially for small carriers like the one involved in this tragic accident.Please advise,thanks!

Answer
Michael

In certain types of accidents an 'improved' fuel tank may be less likely to contribute to a post crash fire, but the economics and practicality of such a retrofit would surely to be expensive to cost prohibitive. Especially at the level of the small on demand charter operators utilizing piston aircraft, a government mandated modification could be costly enough to put some out of business. A fuel tank modification as you suggest cannot be easily justified as a necessary mandatory safety modification for general aviation such as, for example, airbags for automobiles were. Most often, the cause of a crash was one, if not a few, preventable errors. Correcting and preventing the error chain is a more cost effective and realistic solution than taking steps to modify fuel tanks in an effort to control a fireball that may or may not even happen.

In addition, any such aircraft modification would require governmental approval and issuance of a supplemental type certificate. When an aircraft like the Piper Navajo was manufactured it's design was tested and approved by the Federal Aviation Administration under Part 23 of the Federal Aviation Regulations.

http://en.wikipedia.org/wiki/Type_certificate
http://en.wikipedia.org/wiki/Federal_Aviation_Regulations

In order to modify an aircraft from it's original approved design under Part 23, a supplemental type certificate (STC) must be issued. An STC is an aircraft type certificate/TC that is issued when an applicant (like a modification vendor) has received FAA approval to modify an aircraft from its original design.  The STC, which incorporates by reference the related original TC, approves not only the modification but also how that modification affects the original design.

Unfortunately, most crash resistant fuel system designs seem to mostly be military and/or for rotorcraft. That said, there are a few options on the market for fixed wing operators who might elect to have a "self-sealing" or a "crash resistant" fuel cell installed in their current aircraft. (FFC, Inc of Memphis TN has several designs and the STC for several general aviation.)

In addition, there has been some research, testing and even application by certain operators (mostly military) of aviation fuels with improved fire safety like gel fuel or efforts at rendering fuel vapor in aircraft tanks as non-combustible to reduce or prevent fuel fires in aircraft crashes. Changing the fuel the industry uses in the future might be a better safety focus than trying to modify the old aircraft as the safety benefits are much farther reaching to numerous aircraft types:

"The reduction of the fire hazard of fuel is critical to improving survivability in impact-survivable aircraft accidents. Despite current fire prevention and mitigation approaches, fuel flammability can overwhelm post-crash fire scenarios. [A] Workshop on Aviation Fuels with Improved Fire Safety was held in November 1996 to review the state of development, technological needs, and promising technology for the future development of aviation fuels that are most resistant to ignition during a crash." The resulting book on the findings of this conference is a summary of workshop discussions and 11 presented papers in the areas of fuel and additive technologies, aircraft fuel system requirements, and the characterization of fuel fires."  - National Research Council (U.S.). Committee on Aviation Fuels

Get the eBook here- http://www.nap.edu/catalog.php?record_id=5871

Regards,
D.