Petition for Exemption 

Bombardier Inc. 

Uncontrollable High Thrust Failure Conditions 

Model BD-100-1A10 

Relief from section 14 CFR Part 25.901(c) 

SUMMARY 

Sections of the Regulation Affected: 

14CFR §25.901(c) 

Description of Relief Sought: 

Time Limited Exemption of Bombardier BD-100-1A10 Aircraft from the 14CFR § 25.901(c) 

requirement as it relates to certain extremely remote uncontrollable high thrust failure 

conditions. 

Text of Requirement for which Exemption is Sought: 

14 CFR §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. 
June 20, 2014 AW-BD1/14/435 

Bombardier Aerospace respectfully requests a time limited exemption to the Federal Aviation 

Regulation (FAR) Part 25.901(c) of Title 14, CFR, for certain extremely improbable powerplant 

failures that could affect, under determined simultaneously converging conditions, a very limited 

portion of the flight envelope of the improved Bombardier BD-100-1A10 equiped with the 

Honeywell AS907-2-1A engine, also known as Challenger 350. 

The exemption is required for a period of 4 years after FAA validation. During this period, 

Bombardier and Honeywell will develop and make available an improved Uncontrollable High 

Thrust (UHT) logic which will mitigate the effects of an UHT event. The improvement will be 

certified prior to the expiration of the time frame specified above and will be implemented in all 

production aircraft incorporating the AS907-2-1A engine. 

The nature of this petition for exemption is similar to previously granted exemptions 

for the Airbus models A340-500, A340-600, the Embraer models EMB-135BJ, EMB145XR, the Boeing model 757-300 and 777’s and the Gulfstream Models G150, G-1159, 

G-IV, GV, GV-SP and G280. 

Justification 

Bombardier has shown in the position to the TCCA Issue Paper P-01 that the overall 

level of safety of the thrust control system of the Challenger 350 will not be less than that of the 

current BD-100-1A10 fleet. This fleet has never had an UHT event since its entry into service 

back in 2003. However, full compliance with 14 CFR 25.901(c) would require introduction of 

complicated and novel design changes to the BD-100-1A10. It is recognized that experience 

over the past few years has demonstrated that some solutions can safely and reliably eliminate 

the likelihood of a single failure or combination of failures leading to an UHT event that will 

jeopardize the safe operation of the airplane. At this time Bombardier is assessing which design 

solution to incorporate in the BD-100-1A10 aircraft to eliminate most, if not all, UHT failure 

effects to the aircraft safety. 

Issue of Public Interest 

A control system design change that will keep the aircraft controllable for all UHT failure modes 

of concern for the Bombardier BD-100-1A10 would require significant modifications to the 

current engine control system. Since this feature is still in development, such redesign would 

prevent Bombardier from certifying the Challenger 350 design changes on a timely and 

competitive schedule, putting it in an unfair disadvantage to its competitors and directly affecting 

its US customers. 

Additionally, requiring the BD-100-1A10 model to fully comply with this rule would adversely 

affect US companies involved in the design and production of the aircraft. 

Effect of the Exemption on Safety 

As stated above and demonstrated to the authorities by analysis, the risks due to uncontrollable 

high thrust failure conditions on the improved BD-100-1A10/AS907-2-1A will not exceed those 

for the current BD-100-1A10 (equipped with the AS907-1-1A engine) and for the currently 

known and accepted comparable existing transport category airplanes. This means that 

granting this exemption should not adversely affect safety within the current transport airplane 

fleet. 

The conditions under which an uncontrollable high thrust failure may jeopardize the safe 

operation of the airplane are limited to specific conditions during takeoff and landing scenarios. 

This limited exposure, in conjunction with the low probability of occurrence, means that an 
June 20, 2014 AW-BD1/14/435 

Uncontrolled High Thrust event is a very low risk per flight hour. Also, given that one of these 

scenarios occurs, there are still limited risks that any serious injury will develop. This 

assessment is supported by the fact that the 1997 Saudi Arabian Airlines Boeing 737-200 

accident is the only one attributed to these types of failures and there were no serious injuries in 

that accident. 

Waiver of Notice and Public Procedure 

Bombardier respectfully requests that action on this petition should not be delayed by 

publication and comment procedures. Bombardier believes that the existence of numerous 

previous granted similar exemptions justifies this request. 

Conclusion 

Bombardier believes that the above arguments favor a time limited exemption from 14 CFR 

25.901(c) for the aft fuselage mounted installation of the Honeywell FADEC controlled engines 

onto the Challenger 350 aircraft. Additionally, Bombardier believes that any risks due to an 

Uncontrollable High Thrust failure condition on the Challenger 350 will not exceed those 

currently known and accepted for the current aircraft configuration and for those of comparable 

existing transport category airplanes and that an exemption is in the public interest. Bombardier 

requests that the privileges of this exemption would apply outside the United States due to the 

transoceanic capability of the BD-100-1A10 aircraft and the character of mission for many of our 

operators. 

John Kotnjek 

Manager, Airworthiness