GCF-0129/2011 – 2/6

Summary 

Petitioner: Embraer S/A 

Section of the Regulation Affected: 14CFR 25.954 and 25.901(c), amendment 124. 

Description of Relief Sought: Embraer’s petition for a time-limited exemption from 

14CFR 25.954 and 25.901(c) for the auxiliary fuel tanks vent system of the EMB-135BJ 

modified in accordance with the Design Change Approval (DCA) 0145-000-00020-2008 

Rev E (Legacy 650). 
GCF-0129/2011 – 3/6

Embraer respectfully submits the enclosed petition for a time-limited exemption from the 

provisions of 14CFR 25.954 and 25.901(c) as they apply for the auxiliary fuel tanks vent 

system of the Legacy 650 airplane, including those that incorporate flame arrestors. 

Text of the Requirements for which exemption is sought 

14CFR 25.954 “Fuel system lightning protection” 

“The fuel system must be designed and arranged to prevent the ignition of fuel vapor 

within the system by— 

(a) Direct lightning strikes to areas having a high probability of stroke attachment; 

(b) Swept lightning strokes to areas where swept strokes are highly probable; and 

(c) Corona and streamering at fuel vent outlets.” 

14CFR 25.901 ”Installation” 

(c) For each powerplant and auxiliary power unit installation, it must be 

established that no single failure or malfunction or probable combination of 

failures will jeopardize the safe operation of the airplane except that the failure of 

structural elements need not be considered if the probability of such failure is 

extremely remote. 

Background

The Legacy 650 design retains auxiliary fuel tank vent system design concepts 

previously approved on other EMB 135/145 model airplanes. However, the previously 

accepted means of demonstrating compliance was just recently found to be deficient in 

some respects. As a result, it is impractical to demonstrate compliance with 14 CFR 

25.954 and 25.901(c) in a timely manner for the Legacy 650. Embraer requests that this 

time-limited exemption be granted until unequivocal demonstration of the safety and 

compliance with the afore mentioned requirements is achieved through more detailed 

evaluation of the system and results of testing whose procedures shall be guided and 

approved by the FAA. 

Some aspects of the proposed design and means of compliance that have been 

brought into question include: 

• Adequacy of the means used to demonstrate the effects of lightning attachments 

to vent outlets 

• Potential for bypass valves to allow flames to bypass a flame arrestor, either 

under nominal or foreseeable failure conditions. 

• Potential for hazardous ignition of fuel vapors within the tank vents used for 

refueling on ground, either under nominal or foreseeable failure conditions. 
GCF-0129/2011 – 4/6

Embraer offers the following justification in support of this exemption, as well as, 

substantiation as to why the current design provides an adequate level of safety for the 

interim period of this exemption and why granting it is in the public interest, as required 

by 14 CFR 11.81.

Grounds Supporting Exemption

There are two models of flame arrestors installed in the auxiliary tanks of the Legacy 

650: 

- The forward and aft tanks use a circular shaped model, with no bypass valves; 

- The ventral tank that is being included uses a rectangular shaped model that has 

two bypass valves; 

Both models have the same honeycomb as the arresting element, being 2 inches long 

for the rectangular one and 1 inch long for the circular. The rectangular one has been 

certified at lightning strike zone 2A (more than 100 EMB-145XR airplanes flying with 

identical installation setup for accumulated 1.93 million hours) and the circular model 

has been certified for the baseline airplane EMB-135BJ – Legacy 600 in an identical 

installation at a lightning strike zone 2A (more than 150 airplanes flying for accumulated 

373 thousand hours). There is no record of damage due to lightning strikes on fuel 

system of these more than 250 airplanes that have flown more than 2.4 million hours. 

These flame arrestors models have passed a flame holding tests for at least 2.5 

minutes (as required in the Special Condition IP P-9 – Fuel Vent System Fire Protection 

document, Project #TC0714AT-T – EMB-145). 

Similar models have been subjected to lightning strike testing using Zone 2A threat 

levels as defined in the AC 20-53. 

While Embraer has successfully used this method in the past, we were recently 

informed by the certification authorities that to find compliance with the 25.954 

requirement additional testing and/or analysis would be required. 

However, currently there is no formal standard, policy or guidance from the authorities 

as to how this additional testing and/or analysis should be performed. Therefore time is 

required to reach agreement on mean of compliance and perform the additional testing 

and/or analysis. 

Embraer intends to perform the tests by the end of October 2011 on the auxiliary tanks 

vent, but the actual timeframe depends upon the test guideline be provided. Regarding 

the test articles, Embraer intends to test the current design of vent outlets with the 

current flame arrestors and in what regards the bypass valves, with them open, 

simulating their fault. 
GCF-0129/2011 – 5/6

Embraer requests a provision for up to 3 years from the date of granting this exemption 

should design changes be necessary. Such design changes would be incorporated into 

production and service instructions provided within these three years. 

It is important to note that the probability of a lightning strike to attach to a vent outlet is 

very low, given the vents areas by total zone 2 area ratio is 2.16 x 10-5 (this can be 

assessed as the distribution of the lightning strikes is randomly spread, being the vent 

outlets not a ‘preferred’ attachment point as they are not protruding from the fuselage 

skin) and that the probability of a lightning to strike the EMB-145 aircraft (from service 

data) is 5.67 x 10-4 per flight which gives an overall probability of 1.22 x 10-8. This leads 

to, given the auxiliary tanks of the Legacy 650 have been demonstrated to have low 

flammability levels (around 3%), to a probability of ignition of the effluent from the vents 

is in the order of 10-9. 

This way, the design aspects that have been found impractical to demonstrate 

compliance with those requirements, considering the very low probability of incidence of 

lightning strikes and flammability levels, provide adequate safety levels for the auxiliary 

tanks vent against ignition from lightning strikes, within the time period of this 

exemption. 

Issue of Public Interest 

Denial of this petition for exemption would result in the delay in certification and delivery 

of the Legacy 650 to the United States (U.S.). Although these airplanes are not 

manufactured in the U. S., a significant portion of the airplane, including the engines, 

avionics, interiors and the fuel system parts are supplied by U.S. manufacturers. Denial 

of this exemption request would result in the loss of revenue for these U.S. 

manufacturers and have an adverse impact on the U.S. balance of trade, both of which 

are counter to the public interest. 

In addition, our U.S. customers have made fleet schedule plans based on the agreedupon delivery schedule of these airplanes. To require Embraer to modify these 

airplanes prior to service entry will unavoidably delay delivery and have an adverse 

financial effect on these operators. This action would be counter to the public interest. 

Request to Forego Publication in the Federal Register 

Because the flame arrestor installation in the Legacy 650 is identical to those found in 

other airplanes in service, the granting of this exemption to 14 CFR § 25.954 and § 

25.901(c) would create no precedent compared to previous models, both from Embraer 

and other manufacturers, that have been certified without exemptions. In addition, this 

petition requests only 12 months to complete the tests and assessments for the 
GCF-0129/2011 – 6/6

identified aspects. Accordingly, Embraer requests that the FAA does not delay granting 

of this exemption for publication of the petition summary in the Federal Register as 

allowed by 14 CFR §11.87. 

Embraer has a contract with an U.S. operator to deliver the first Legacy 650 by the end 

of December 2010 that has already been delayed to middle February due to the 

certification process. As above mentioned, more delays in the delivery will adversely 

affect this operator forcing him to seek alternatives to his planned use of the airplane, 

such as canceling scheduled flights, chartering alternative lift, etc. or even canceling the 

contract. 

Embraer also notes that this petition was filed immediately after identified the 

impracticability of FAA in finding the compliance. 

In summary, there exists the necessary justification for forgoing publication of a petition 

summary in the Federal Register, and Embraer respectfully requests that grant this 

petition without delay. 

Effect of the Exemption on Safety 

The entire EMB-145XR and Legacy 600 fleet (more than 250 airplanes worldwide) have 

the same auxiliary tank fuel vents as the Legacy 650. There are more than 140 of such 

airplanes currently operating safely within the U.S. territory for over 8 (eight) years and 

are expected to continue to do so for many years to come. Eight airplanes are expected 

to be delivered within the first 12 months. If compliance is found there would have been 

no effect on safety. If modifications are required at most a total of 25 aircraft would have 

been added to the current fleet within the three years of this exemption. Therefore, 

granting this exemption will not significantly affect the overall safety of the U.S. fleet, as 

the contributions of the accumulated hours of the 25 more airplanes (that have low 

utilization typical of such business jets) with a similar level of risk to that fleet, clearly 

represent a negligible impact on the total fleet safety. 

Operations Outside the United States

As a manufacturer and not an operator, Embraer does not intend to operate outside the 

United States under the terms of the exemption which we are requesting, but some of 

our operators will certainly fly the Legacy 650 internationally. The granting of this 

petition will not conflict with any of the terms of ICAO Annex 8, so the FAA will not need 

to file a difference with ICAO, as described in 51 1.83.