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### August 12, 2013

AW-BD5/13/503

Mr. Gaetano Sciortino Manager, New York Aircraft Certification Office

Federal Aviation Administration

1600 Stewart Avenue Westbury, New York

U.S.A 11590

Attention: Mr. Serge Napoleon, Project Manager

Subject : CSeries airplane models BD-500-1A 10 (CS100) & BD-500-1A11 (CS300) – BA response to FAA letter dated April 30 th 

### , 2013 regarding petition for Exemption per 14CFR § 11.61(b) from 14CFR § 25.841(a) (2) with respect to Uncontained Engine Failures.

References: (1) BA Letter AW-BD5/11/693, titled “BD-500-1A10 & 1-A11 (CSeries CS100 & CS300) – Petition for Exemption from CAR 521.30(1)(e) for 14CFR § 25.841(a)(2) with respect to Uncontaine d Engine Failures”, dated 2011-10-19. (2) FAA-BD5_2013-04-30 - FAA Request fo r Additional Information for Exemption from 841(a)(2) for UEFs - FAA-2012-1146-0005

Dear Mr. Napoleon,

The Bombardier Aerospace (BA) petition for exemp tion from the requirements of Title 14, Code of Federal Regulations (14 CFR) 25.841(a)(2)(i) and (a)(2)(ii) at Amendment 25-87 for the Bombardier Models BD-500-1A10 (CS100) a nd BD-500-1A11 (CS300) was submitted to the Federal Aviation Administration (FAA) on Nove mber 9, 2012 [see reference (1)]. The FAA review of the BA petition is complete and FAA has requested additional information prior to granting the exemption which has been cap tured in the FAA letter dated April 30 th 

### , 2013 [see reference (2)].

Enclosed with this letter is th e BA response to the FAA request.

Should you require additional information, pleas e contact Carina Groom bridge at (514) 855- 5000 x 63773 or carina.groombridge@aero.bombardier.com.

Yours truly,

Keith Barnett Airworthiness Manager, CSeries Bombardier Aerospace HEADQUARTERS

BOMBARDIER AEROSPACE 400 CÔTE-VERTU ROAD WEST DORVAL, QUÉBEC CANADA H4S 1Y9

TEL. 514-855-5000

FAX. 514-855-7401

www.bombardier.com

### Bombardier Airworthiness Coordination

BA Reply to FAA Letter dated April 30, 2013 Page 1 of 3 Subject : BA Response to FAA Letter dated April 30, 2013.

Reference(s) : 1. Airworthiness – CSeries Certification eRoom Action Item #2545. 2. BA Letter AW-BD5/12/530, titled “Petition for Exemption per 14CFR § 11.61(b) from 14CFR § 25.841(a)(2) with respect to Uncontained Engine Failures”, dated October 1 st , 2012. 3. Minutes of Meeting (BA/FAA/TCCA) dated on 2013-06-07. 4. BA Memo RMAS-2013-BD500-MEMO-135 Rev. -2, titled “Fuselage Hole Size vs. Rotor Burst Damage Probability”, dated July 09, 2013. 5. Supplier (P&W) Report MBR-PW500-137 Rev. --, titled “PW/500G Engine Rotor Burst Near Field Damage Assessment”, dated 2012-06-08. 6. FAA AC No. 20-128A, titled “Design Considerations for Minimizing Hazards Caused by Uncontained Turbine Engine and Auxiliary Power Unity Rotor Failure”, dated on March 25, 1997. 7. Supplier (LTS) Report T-C08110300-DAC-0001 Issue 4, titled “CPCS Cabin Depressurization Analysis CSeries (BD500)”, dated December 21,

2010. 8. FAA Policy Memorandum ANM-03-112-16, titled “Interim Policy on High Altitude Cabin Decompression (Reference Amendment 25-87)”, dated March 24, 2006. 9. BA Memo FS-2009-BD500-109-EPB, titled “Aerodynamic Data for Climb/Descent Performance and Mission Profiles”, dated 2010-08-19. 10. BA Report RAE-BA500-023 Rev. D, titled “Crew Interface Design Document for Auto Flight”, dated 2012-05-09. 11. FAA-BD5_2013-04-30 - FAA Request for Additional Information for Exemption from 841(a)(2) for UEFs - FAA-2012-1146-0005

BA Position:

Bombardier Aerospace (BA) acknowledges FAA’s request for additional information [per reference 11] to support BA’s petition [per reference 2] for an exemption per 14CFR 11.61(b) from 14CFR 25.841(a)(2) with respect to Uncontained Engine Failures (UEF). BA has prepared the following response, which was organized to address each question, in the order presented in the FAA’s letter [reference 11], to fulfill the need for specific data, taking into account BA/FAA related discussions, as recorded in reference 3.

Question/Request (1)

Information on: 1. Resulting holes from UEF events versus probability of occurrence: Reference 4 summarizes BA analysis on geometry probability of occurrence of UEF events taking into account a specific hole size and applicable engine rotor definition (see reference 5 for further details). Such a document includes attachments that provides the details about the dimensions used to define the cut areas, which in turn define the respective hole sizes. Reference 6 provides more details on actual adopted methodology and assumptions. Now, for the actual probability of occurrence per flight hour, the numbers presented in reference 4 should be combined with the probability of an UEF event in cruise at high altitude to achieve such a number. In the original BA’s request/petition for the exemption, a

### Bombardier Airworthiness Coordination

BA Reply to FAA Letter dated April 30, 2013 Page 2 of 3 conservative approach was adopted by simply considering a factor of 0.1 for the probability of occurrence of a significant UEF event, i.e. an event where the rotor fragment could hit the fuselage and, therefore, would cause a depressurization.

2. Decompression analysis (e.g., airplane cabin pressure time history), including critical hole size to meet 14CFR 25.841(a)(2): Reference 7 provides preliminary results for the CSeries Depressurization Analysis, which defines the critical hole sizes to successfully meet the cabin pressure limits contained in 14CFR 25.841(a)(2); presenting the time history for applicable scenarios (i.e. aircraft and cabin pressure profiles). Such a document also provides all the assumptions and references taken into account for the analysis. It shall be noted, however, that such an assessment, which takes into account the predicted aircraft emergency descent rates, is still preliminary and may, therefore, need updating upon the finalization/demonstration of actual final aircraft performance.

Question/Request (2)

BA has taken the FAA’s request into account and plan to develop, in partnership with BA’s Oxygen System supplier, the applicable substantiati on material (i.e. assessment of the severity of a depressurization to the occupants). Initial discussions with such a supplier indicate that preliminary data will be made available in 4Q2013 (or earlier if possible). Such an assessment intends to address the severity of a depressurization to Crewmembers and Passengers, taking into account the aircraft performance (slowest applicable emergency descent profile, but still in compliance with reference 8) and considering that the aircraft occupant may have or not don

her/his mask in time.

Question/Request (3)

BA concurs with the FAA that the “primary means to ensure occupant survivability (following a rapid depressurization event) rests in quickly bringing the occupants to a cabin pressure where they can survive (i.e., a lower cabin pressure altitude)”.

In that sense, and as indicated in the original request/petition for an exemption, BA will demonstrate that the CSeries aircraft is capable of meeting or exceeding (by being faster) the descent performance established by reference 8, such that occupants will not be exposed to

cabin altitudes:

a) above 45,000 ft for any amount of time; b) above 40,000 ft for more than one minute; c) above 25,000 ft for more than three minutes; and d) above 10,000 ft for more than six minutes.

It shall be noted, however, that in demonstrating the descent capability of the aeroplane in order to meet applicable cabin altitude profile, only the loss of the failed engine’s power related systems affecting the descent will be considered (i.e. if losing power on one engine results in loss of one hydraulic system engine-driven-pum p, the descent rate will be based on the capabilities of the remaining hydraulic systems with the backup power sources, such as the ACMP or PTU). Systems degradation due to the actual UEF’s debris damage trajectory (e.g. hydraulic line rupture, wiring damage, etc.) will not be considered.

### Bombardier Airworthiness Coordination

BA Reply to FAA Letter dated April 30, 2013 Page 3 of 3 Furthermore, it shall also be noted that although having other design features, such as Emergency Descent Mode (EDM), that may provide additional margin of safety, the intent is to demonstrate that the aircraft can be descended accordingly and independently by relying mainly on pilot action and no credit will be taken for EDM; reason why no information on EDM has been provided in the original request/petition for the exemption.

Question/Request (4)

As far as the CSeries aircraft emergency descent performance is concerned, BA reiterates that the intended approach is to substantiate through, first, analysis [see reference 9 for preliminary performance], and then, flight testing; that the airplane can descend in a rapid manner such that will meet the requirements established in reference 8.

Question/Request (5)

As requested, please find herein the description of the EDM feature for the CSeries aircraft (models BD-500-1A10 and BD-500-1A11):

The CSeries EDM feature is a part of the Auto-Flight System. In automatic mode, it is designed to engage any time the cabin altitude warning is posted (at 10,000 ft for non-HAAO and up to 14,500 ft for HAAO), provided it is armed (EDM guarded momentary PBA pushed) and the aircraft altitude is above 25,000 ft. Once engaged, it can easily be disengaged, by the pilots, by

either: 1. Disconnecting the auto pilot (A/P) and taking manual control; or 2. Pushing the EDM PBA. In this case, EDM will be cancelled but the A/P will remain engaged.

Reference 10 provides for further details on the design of such a feature, including its operation

in manual mode.

DISCIPLINE NAME APPROVAL / DATE

Environmental Systems C. Lima

RM&S Focal F. Godin

Airworthiness Focal C. Groombridge

Airworthiness Manager K. Barnett