UNITED STATES OF AMERICA 

DEPARTMENT OF TRANSPORTATION 

FEDERAL AVIATION ADMINISTRATION 

RENTON, WASHINGTON 98057-3356 

In the matter of the petition of 

Exemption No. 16780 

Bombardier Aerospace Regulatory Docket No. FAA-2016-2750 

for an exemption from§ 25.901(c) of 

Title 14, Code ofFederal Regulations 

GRANT OF EXEMPTION 

By letters dated January 13, 2016, and April4, 2016, Mr. Glenn Baxter, C Series Airworthiness 

Manager, Bombardier Aerospace, 400 Cote-Vertu Road West, Dorval, Quebec, H4S 1Y9, 

Canada, petitioned the Federal Aviation Administration (FAA) for an exemption from the 

requirements of§ 25.901(c) of Title 14, Code of Federal Regulations (14 CFR). This exemption, 

if granted, would permit relief from full compliance with the regulation for Model BD-500-1 A1 0 

and BD-500-1A11 airplanes. 

The petitioner requests relief from the following regulation: 

Section 25.90l(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. 

The petitioner supports its request with the following information: 

This section quotes the relevant information from the petitioner's request, with minor edits for 

clarity. The complete petition is available at the Department of Transportation's Federal Docket 

Management System, on the Internet at http://regulations.gov, in Docket No. FAA-2016-2750. 

Description of Relief Sought 

Bombardier Aerospace (Bombardier) respectfully requests a permanent exemption from 

14 CFR 25.901(c) for a certain extremely improbable throttle quadrant assembly (TQA) 

failure that could contribute, under specific simultaneously converging conditions, to an 

engine uncontrolled high thrust (UHT) event under very limited and specific takeoff and 
landing scenarios on the BD-500-1A10 and BD-500-1A11 airplanes (C Series CS100 and 

C Series CS300, respectively). 

This exemption is requested for a permanent period after FAA type validation. Due to 

the small (single) number of failures within the TQA, the limited window of exposure, 

and the practicality of redesigning the TQA (which currently meets the industry norms), 

Bombardier believes permanent relief from§ 25.901(c), relative to the TQA, is 

appropriate. Furthermore, Bombardier understands precedent exists with the FAA for 

this relief, most recently with FAA Exemption No. 10614. 

Justification 

Bombardier has shown in the position to FAA Issue Paper P-25 that the overall level of 

safety of the thrust control system of the C Series CS 100 and CS300 airplanes will not be 

less than that of the current Bombardier transport category aircraft fleet. The Bombardier 

fleet of full authority digital electronic control (F ADEC) equipped aircraft have more than 

16 million aircraft flight hours. This fleet has never had a TQA failure leading to a UHT 

event. Full compliance with§ 25.901(c) would require the introduction of novel design 

features to the BD-500-1A1 0 and BD-500-1A11 airplanes. 

It is recognized that experience over the past few years has demonstrated that some 

design solutions can safely and reliably eliminate the possibility of a single failure or 

combination of failures leading to a UHT event. Bombardier has introduced a thrust 

control malfunction accommodation feature into the engine electronic control to address 

engine failures that may lead to a UHT event and will eliminate all noncompliant, 

uncontrollable, high-thrust failures, except for a very specific case related to the drive 

train failure of the TQA under a high-speed rejected takeoff (RTO) operation. 

Introducing a more complex design into the TQA assembly with the intent of eliminating 

the single failure will introduce more components to the assembly, increasing the 

probability of failure and being counterproductive to both Bombardier's and the FAA's 

goal of continuous improvement in overall aircraft reliability and safety. Such design 

changes may minimize drive train failures but would not eliminate the more likely events 

ofajammed control(s) due to foreign objects, both within the control and externally from 

items on the flight deck. 

Issue of Public Interest 

A thrust control system design change that would keep the aircraft controllable for all 

UHT single system failures would require modifications to the current TQA. 

Implementing this redesign would prevent Bombardier from certifying the C Series 

CS 100 and CS300 design in a timely and competitive schedule, putting it in an unfair 

disadvantage to its competitors and directly affecting its customers in the United States. 

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Additionally, requiring the BD-500-1A10 and BD-500-1A11 models to fully comply with 

this rule would adversely affect United States companies involved in the design and 

production of the aircraft. 

Effect of the Exemption on Safety 

As stated above and as previously demonstrated to the FAA by analysis, the risks due to 

UHT failure conditions on the BD-500-1A10 and BD-500-1A11 aircraft will not exceed 

those of the current Bombardier transport category aircraft fleet, nor the currently known 

and comparable existing transport category airplanes. 

The conditions under which a UHT failure may jeopardize the safe operation of the 

airplane are limited to specific conditions during takeoff and landing scenarios. The 

majority of these scenarios are addressed by the engine thrust control malfunction 

accommodation feature. A UHT event due to a single failure in the TQA has a very low 

risk per flight hour, many orders of magnitude less than that accepted as extremely 

improbable. The Bombardier TQAs have never had a disconnect of the drive train 

between the control lever and the throttle position resolvers. Such a failure will be less 

than extremely remote. 

The Bombardier assessment is that the TQA failure would only become a hazard when 

associated with a high speed RTO. The Bombardier assessment shows that an RTO is an 

independent event from the TQA failure. A high speed RTO not associated with another 

aircraft failure is remote (i.e., due to birds or aircraft failure to clear an active 

runway < 1 E-05). Additionally, in the event of an occurrence, there is limited risk that 

any serious injury will result. 

Conclusion & Request to Extend Privilege of Exemption Outside the United States 

Bombardier believes that the above arguments favor a permanent exemption from 

§ 25.901(c) for the TQA on the BD-500-1A10 and BD-500-1A11 (C Series 100 and 

C Series 300) airplanes. Additionally, Bombardier believes that any risks due to a UHT 

failure condition generated by the TQA single failure case on the subject airplanes will 

not exceed that 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 subject airplanes 

and the character of mission for many of our operators. 

Federal Register publication 

Although the petitioner requested that action on its petition not be delayed for publication in the 

Federal Register, the FAA found that the petition, if granted, would set a precedent. Therefore, 

to allow an opportunity for the public to comment on the petition, a summary of it was published 

in the Federal Register on April 27, 2016 (81 FR 24933). No comments were received. 

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The FAA's analysis 

Introduction 

Bombardier is requesting an exemption from the requirements of§ 25.901(c) as it applies to the 

"no single failure" provision for the throttle quadrant assembly (TQA). Bombardier 

acknowledges that there are single failures of the TQA that could result in UHT under certain 

conditions. They also state that the TQAs on other Bombardier airplanes are of similar design 

methodology and have not had a failure that resulted in UHT. Bombardier contends that a 

redesign to eliminate the TQA drive train failure would add complexity and result in a lessreliable design. Bombardier has provided design details to the FAA demonstrating that they have 

taken all practical measures to eliminate single failures that could result in UHT. Those 

measures include provisions to minimize the potential for internal and external debris as well as 

eliminating all single failures within the TQA, except for a failure of the drive train gears 

resulting in a disconnect with the throttle and potentially causing a UHT event. 

Additional UHT Consideration 

The FAA recently identified a condition in which transport airplanes could become 

uncontrollable during flare about 10 seconds before touchdown if there is a sufficiently strong 

crosswind in combination with a UHT failure and that this condition is endemic to the transport 

airplane fleet. Bombardier has demonstrated that the Model BD-500-1 A 10 and BD-500-1 A 11 

airplanes remain controllable and comply with 25.901(c) in crosswinds up to 15 knots. Since 

Bombardier did not include crosswinds in excess of 15 knots in their assessment and the "no 

single failure" requirement of 25.901 (c) requires applicants to consider operational and 

environmental factors that could intensify a failure, the FAA has determined that this scenario 

should also be included in this grant of exemption. As a result, this exemption also applies to 

UHT landing scenarios that when combined with crosswinds in excess of 15 knots, would 

jeopardize the safe operation of the airplane. 

Public Interest and Effect on Safety 

According to § 11.81, Bombardier must show that granting this request is in the public interest 

and will not adversely affect safety. If the FAA were to deny this petition, it would substantially 

delay delivery of these airplanes and put considerable schedule pressure on the development and 

certification of additional design changes which would not necessarily prove to be more reliable 

and would not have the service history that supports a substantially low failure rate. This would 

not only have adverse economic and logistical impacts for Bombardier, but would also affect 

United States companies involved in the design and production of the airplanes. Therefore, we 

conclude that granting this petition would be in the public interest. 

Bombardier acknowledges in the petition that the Model BD-500-1A10 and BD-500-1Al1 

airplane type design currently proposed for certification will not fully comply with the "no single 

failure" provision of§ 25.901(c) as it relates to certain UHT failure conditions. The 

investigation of a 1997 accident involving a Saudi Arabian Airlines Boeing 737-200 airplane 

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determined that this type of non-compliance had long been endemic in the state-of-the-art engine 

control architectures of most transport category airplanes. Until recently, most type certification 

programs have included some sort of exemption for UHT failure conditions. However, one of 

the conditions for granting each of those exemptions has been that the applicant takes all 

practicable actions to minimize the adverse effects on safety associated with granting the 

exemption. 

The FAA has reviewed the Model BD-500-lAlO and BD-500-lAll type design and 

acknowledges that Bombardier has taken all practicable actions to eliminate or further reduce the 

risks associated with this non-compliance. Specifically, thrust malfunction accommodation logic 

(i.e., logic that identifies and safely accommodates any sustained, substantial discrepancy 

between the actual and commanded thrust, as sensed and validated by the engine control) has 

been implemented for those applicable UHT scenarios. Such thrust malfunction accommodation 

logic incorporated into airplane type designs has proven to be practical and effective at 

eliminating most noncompliant UHT failures except for those associated with the airplane 

throttle system (e.g., stuck throttle or disagreement between the throttle input to the engine 

control and the actual throttle position). 

While some recent airplane throttle system designs have managed to fully comply with 

§ 25.901(c), this has not yet become the industry norm. The Bombardier TQA design includes 

redundant features intended to prevent a stuck throttle at the high power position. The TQA 

design also has robust features intended to prevent the introduction of foreign objects or debris 

into the TQA. Other than debris jamming the TQA, Bombardier has identified only one 

remaining single failure of the drive train gear that could result in a UHT event. Since the 

conditions of this exemption only allow a very low overall predicted UHT occurrence rate, the 

FAA has usually found it is not in the public interest to require these systems be redesigned. 

The conditions under which a UHT failure may jeopardize the safe operation of the airplane are 

limited to specific aborted takeoff or approach-and-landing scenarios. Given that these scenarios 

occur, there is still a low probability that a serious injury will result. This limited exposure, in 

conjunction with the historically low occurrence rates, makes this a relatively low risk per flight 

hour. Bombardier will be required, by the conditions for granting this exemption, to demonstrate 

that the risks due to UHT failure conditions on any airplane certificated under this exemption 

will not exceed those currently known and accepted for comparable existing transport category 

airplanes. Making this a condition of this exemption, in combination with the condition that all 

practical actions are taken to eliminate or further reduce that risk, means that granting this 

exemption should not adversely affect, and in fact should improve, the average per-flight-hour 

risk within the current transport airplane fleet. 

This exemption allows a slightly greater hazard than full compliance with§ 25.901(c) but given 

the fact that the per-flight-hour risks associated with this non-compliance are low and the 

conditions under which a UHT failure is limited to specific aborted takeoff, approach, and 

landing conditions and that if these scenarios occur, there is still a low probability that a serious 

injury will result. The limited exposure, in conjunction with the historically low occurrence rate, 

makes this a relatively low risk per flight hour. The FAA has determined that the proposed 

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exemption provides a level of safety equivalent to that of the existing fleet of similar transport 

airplanes. Therefore, we conclude that granting this petition would not adversely affect safety. 

The FAA's decision 

In consideration of the foregoing, I find that a grant of exemption is in the public interest and will 

not adversely affect safety. Therefore, pursuant to the authority contained in 49 U.S.C. 40113 

and 44701 delegated to me by the Administrator, I grant Bombardier Aerospace an exemption 

from 14 CFR 25.901(c). I grant this exemption to the extent necessary to allow type certification 

of Model BD-500-1A10 and Model BD-500-1A11 airplanes without an exact showing of 

compliance with the "no single failure" requirement of§ 25.901(c) relating to UHT from a single 

failure of the TQA and the previously-described landing scenarios combined with crosswinds in 

excess of 15 knots. 

This exemption is subject to the following conditions and limitations: 

1. For the Model BD-500-1A10 and BD-500-1A11 airplanes, Bombardier must 

demonstrate, in accordance with an FAA-approved Airworthiness Assessment and Risk 

Management Plan that all practicable actions have been taken to minimize the adverse 

effects on safety associated with granting this exemption. These must include, but are not 

limited to, practical actions to eliminate or further reduce the risks by improving designs, 

training, procedures, and instructions for continued airworthiness (ICA). 

2. For the Model BD-500-1A10 and BD-500-1A11 airplanes, Bombardier must 

demonstrate, in accordance with an FAA-approved Airworthiness Assessment and Risk 

Management Plan, that the risks associated with relieving the UHT failure condition from 

the "no single failure" requirement of§ 25.901(c) are no greater than those currently 

known and accepted for comparable airplanes within the current transport fleet. 

Acceptable risk for this provision can be characterized as: 

a. The airplane complies with§ 25.901(c) for any foreseeable UHT failure 

conditions in flight, except possibly during approach below 400 feet; and 

b. The expected frequency of the occurrence of a UHT failure condition is less than 

once per 1 0 million airplane flight hours. 

3. The following "Note" will be added to the Model BD-500-1A10 and BD-500-1A11 type 

certificate data sheet for any airplane certificated under this exemption: 

The FAA has concluded that the occurrence of any uncontrollable highthrust failure condition, or any of the associated causal failures listed within 

Bombardier Aerospace Document [reference TBD], may endanger the safe 

operation of an airplane. Consequently, the FAA recommends that 

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operators be encouraged to report any such failures in accordance with 

Title 14, Code of Federal Regulations 121.703(c), 125.409(c), and 135.415(c). 

4. In support of the "Note" in condition 3 above, Bombardier must develop the document 

referenced in condition 3 and obtain FAA approval prior to United States customer 

delivery of the BD-500-lAl 0 and BD-500-lAll airplanes. That document will list the 

failures that can contribute to or cause a UHT failure condition covered under this 

exemption. This document will ultimately be made available as part of the I CA. 

Furthermore, for any airplane certificated under this exemption, failures of the type listed 

within that document must be promptly reported to the FAA. The reporting method and 

report timeliness requirements should be the same as those for reporting events under 14 

CFR 21.3. 

The granting of this exemption does not relieve any regulatory obligation to identify and correct 

unsafe conditions related to UHT failure conditions. 

Issued in Renton, Washington, on JUN 1 0 2016 

~~ 

Michael Kaszycki 

Assistant Manager, Transport Airplane Directorate 

Aircraft Certification Service 

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