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May 06, 2013

Ron McCormick

5421 Horse Ridge Way

Bonita, CA 91902

ram.ou812@gmail.com / (619) 434-1905

§ 11.71 What information must I include in my petition for rulemaking?

(a) You must include the following information in your petition for rulemaking:

(2) An explanation of your proposed action and its purpose.

This proposed action is to replace the elastomeric seals now used for fire barrier sealing 

of the inner fixed structure (IFS) portion of aircraft nacelles, with a metallic seal system,

specifically in high operating temperature (<500°F) areas. Some regions of the engine 

compartment of turbine engine aircraft measure temperatures in the range of 625°F and 

above. Elastomeric seals – after exposure to operating cycles (time and temperature) –

can only withstand temperatures below 500°F.

(3) The language you propose for a new or amended rule, or the language you 

would remove from a current rule.

Replace the currently utilized elastomeric seals with a metallic seal system for sealing 

the IFS portion of typical clamshell nacelles of commercial turbine engine aircraft, 

specifically where operating temperatures reach above 500°F.

(4) An explanation of why your proposed action would be in the public 

interest.

The current seal fire tests are performed using ’virgin’ seals that have not been exposed 

to a true operating life cycle (time and temperature). Seal life is determined by exposure 

to both high and low temperatures for a selected period of time. Elastomeric seals can 

only withstand approximately 480°F before degradation and permanent damage occurs. 

There is a known risk of using elastomeric seals, regardless of their material 

composition, when operating temperatures reach above 500°F. The properties of the 

elastomers degrade and can reach a point where they fail as a seal and fire barrier. This 

failure can lead to pressure loss, leakage and other conditions that may compromise the 

performance and safety of the aircraft.

Replacing these elastomeric seals with a metallic seal system that can withstand high 

operating temperatures - with no degradation of any kind, and maintaining full 

functionality - will remedy the risks the elastomeric seals pose.
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(5) Information and arguments that support your proposed action, including 

relevant technical and scientific data available to you.

A metallic seal system has been designed and proven to function as well as elastomeric 

seals, without the risk of degradation and/or damage due high operating temperatures.

Metallic seals, known as spring or turkey-feather seals, have been used as fire barriers 

on aircraft nacelles, exhausts and other areas for several years. The material properties 

of alloys such as INCONEL have proven to be most effective in these applications. 

These alloys are able to withstand temperatures well above 500° F. In fact, AC20-135 

6.d. (6) considers the use of these alloys as acceptable to use without additional fire 

tests required.

Conversely, as a matter of fact, elastomeric seals cannot withstand operating 

temperatures above 500°F. Seal manufacturers state that at sustained temperatures 

above 500°F, the material properties of these seals – even with added flame resistant 

fiber such as Nomex – degrade and irreversibly break down, rendering the seal useless. 

Also, during required seal fire testing, elastomeric seals potentially produce outgasses 

and cause backside ignition – which constitutes test failure.

(6) Any specific facts or circumstances that support or demonstrate the need 

for the action you propose.

The current seal fire tests are performed using ’virgin’ seals that have not been exposed 

to a true operating life cycle (time and temperature). To date, fire seal testing of 

elastomeric seals has resulted in high failure rates, due to the composition of the seals. 

When silicone is burned in air or oxygen, it forms solid silica (silicon dioxide) as a white 

powder, char, and various gases. The readily dispersed powder is sometimes called 

silica fume. This process does not lend itself well in a potential fire environment on an 

aircraft.

The various manufacturers of elastomeric seals admit that – to date – elastomeric seals 

are NOT recommended when temperatures reach 500°F or above. In fact, a VP of one 

major elastomeric seal manufacturer states that these high temperatures require 

metallic seals.

(b) In the process of considering your petition, we may ask that you provide 

information or data available to you about the following:

(1) The costs and benefits of your proposed action to society in general, and 

identifiable groups within society in particular.

The cost of the proposed metallic seal system to replace elastomeric seals is much 

less. Simple manufacturing and tooling requirement, as opposed to the complex 

manufacturing and costly tooling of the elastomeric seals, greatly reduces the overall 

cost. 

Although the elastomeric seals are expected to last the life of the aircraft, many issues 

that may occur negate this expectation. Due to the composition of the elastomeric seals 
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and installation processes, the seals may get damaged and need replacement. Also, if 

the seals are exposed to temperatures over 500 degrees F for a prolonged length of 

time, the seals will need replacement.

The reduced costs of the metallic seal system can very easily convert to lower airline 

costs and reduction of safety concerns to the consumer. 

(2) The regulatory burden of your proposed action on small businesses, small 

organizations, small governmental jurisdictions, and Indian tribes.

n/a

(3) The recordkeeping and reporting burdens of your proposed action and whom 

the burdens would affect.

n/a

(4) The effect of your proposed action on the quality of the natural and social 

environments.

Elastomeric seal manufacturing, as well as the required testing constitutes a much 

larger carbon footprint than the proposed metallic seal system.