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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-500-1A10 (CS100) & BD-500-1A11 (CS300) – BA 

response to FAA letter dated April 30th, 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 Uncontained Engine Failures”, dated 2011-10-19. 

(2) FAA-BD5_2013-04-30 - FAA Request for Additional Information for 

Exemption from 841(a)(2) for UEFs - FAA-2012-1146-0005 

 

Dear Mr. Napoleon, 

The Bombardier Aerospace (BA) petition for exemption 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) and BD-500-1A11 (CS300) was submitted to the 

Federal Aviation Administration (FAA) on November 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 captured in the FAA letter dated April 30th, 2013 [see 

reference (2)]. 

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

Should you require additional information, please contact Carina Groombridge 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 1st, 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 substantiation 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-pump, 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