1

Transport Airplane Directorate

1601 Lind Avenue, S.W.

Renton, Washington 98057-3356

April 30, 2013

Mr. Keith Barnett

Airworthiness Manager, CSeries

Bombardier Aerospace

400 CÔTE-VERTU Rd. West

Dorval, QUÉBEC, Canada H4S 1Y9

Dear Mr. Barnett;

The Federal Aviation Administration (FAA) has completed our review of your petition for 

exemption from 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) airplanes, dated November 9, 2012. 

The exemption, if granted, would provide relief from cabin decompression requirements 

following an uncontained engine failure enabling these model airplanes to operate where 

they are most efficient, thereby reducing fuel burn and producing lower emissions. We have 

determined that we need more information before we can process your petition. Please note

that we have asked for similar information from other petitioners on past petitions for 

exemption to this rule. 

Bombardier is asked to provide the following information: 

(1) On page 2 of 2, Bombardier states that, “The CSeries will meet requirements of 14 CFR 

§ 25.841(a)(2)(i) and (ii) for all system and structural failures but not for all types of engine 

failures; for some UEFs that result in pressure vessel penetration by fragments causing a 

very large hole, the design of the CSeries does not meet the requirements of 14 CFR § 

25.841(a)(2)(i) and (ii). ....”

Question/Request: FAA acceptance of the increased level of risk from a rapid 

decompression is predicated on the probability of the failure event. While Bombardier did 

include some estimates of probability of uncontained engine debris, the Bombardier petition 

did not include any information on the resulting holes from uncontained engine failures 

versus probability of occurrence (e.g., hole sizes versus probability of rapid decompression 

event per flight hour or departure). Bombardier provided no results of their decompression 

analysis (e.g., airplane cabin pressure time history) or comparisons with data from 

uncontained engine debris trajectory studies. Bombardier did not provide an estimate of the 

critical hole size which would result in a decompression which the airplane would 

successfully meet the cabin pressure limits contained in 14 CFR 25.841(a)(2). Bombardier
2

did not provide any estimates of the resulting fuselage hole size versus probability of 

occurrence.

(2) On several pages Bombardier refers to the Aviation Rulemaking Advisory Committee 

(ARAC) Mechanical Systems Harmonization Working Group (MSHWG) report, but 

nowhere in the petition does Bombardier provide an assessment of the severity of the 

depressurization to the occupants as recommended within that report. 

Question/Request: FAA has requested that all petitions for exemption to § 25.841 follow 

the general guidance in FAA Policy Memorandum ANM-03-112-16, Interim Policy on High 

Altitude Cabin Decompression (Reference Amendment 25-87). Within the guidance, FAA 

describes the use of a physiological model that affords some measure of the severity to the 

occupants from a rapid decompression. We have requested that all petitioners utilize models 

similar to those from the ARAC MSHWG Report on § 25.841(a)(2) and (3), August 2003. 

Bombardier did not provide any estimates of the severity to the occupants (e.g., the 

Depressurization Exposure Integral (DEI) method in the ARAC MSHWG Report).

Bombardier should provide this material. 

(3) In the petition Bombardier states that “.... BA has incorporated design features that 

appropriately address the risk to safety following an UEF, as recommended by the FAA 

Interim Policy above. In the unlikely event of an UEF, the CSeries preserves an even higher 

level of safety relative to previously certificated airplanes due to its higher descent 

capability (in line with the time-above-altitude FAA guidance and the recommendations of 

the ARAC), and other design feature such as an Emergency Descent Mode (EDM) which 

will provide an additional margin of safety by initiating a descent automatically if there is 

no flight crew action following a loss of cabin pressure, as well as an automatic pressure 

demand mask (FAA approved for 41,000 ft.) for the pilots which will be certified to comply 

with 14CFR § 25.1441(d). .....”

Question/Request: 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). Policy Memo ANM-03-112-16

requests that, “The petitioner should provide information about any existing or new design 

features that provide enhanced airplane emergency descent rates and occupant 

survivability.” Bombardier has not provided many details on mitigating design and/or 

operational features that offset the increased level of risk at high altitudes (e.g., Does the 

CSeries incorporate any redundant systems that provide additional descent speed capability,

or include additional containment protection from engine debris, etc.?) and, Bombardier did 

not provide any estimated descent speed data or cabin pressure exposure plots (i.e., cabin 

pressure altitude versus time and airplane flight pressure altitude versus time) following 

worst case uncontained engine rotor failure events. Please include all assumptions that have 

been used in the analysis (e.g., hole size, environmental control system pack operation, 

available hydraulic/electrical/pneumatic power to operate control surfaces, discharge 

coefficient of hole, other airplane leakage, etc.). In addition, Bombardier did not provide any

estimated airplane descent rates which cover the operating envelope (e.g., boundaries set by 

maximum and minimum airplane weight). Also, Bombardier did not provide any airplane 
3

performance predictions to show that the CSeries can successfully meet the cabin pressure 

exposure limits in the Policy Memo ANM-03-112-16. 

(4) Bombardier is asked to confirm their intention to conduct flight test certification 

demonstration of the proposed flight test emergency descent procedures (both manual and 

EDM) recommended in the AFM, per Policy Memo ANM-03-112-16. 

(5) On page 12 of 14, Bombardier states, “... h) The CSeries will have an Emergency 

Descent Mode (EDM) which will provide an additional margin of safety by initiating a 

descent automatically if there is no flight crew action following a loss of cabin pressure or 

when the flight crew pushes the EDM button. ....”

Question/Request: Bombardier is asked to provide additional information on the EDM 

system. Please provide an explanation of associated hardware and software architecture, 

system reliability, means to exclude false activation, etc. 

Please do not post proprietary information on the Regulations.gov public website. Either 

mail it to us by certified mail or fax it to us at 425-227-1320

Please provide the supplemental information for Bombardier Models BD-500-1A10 

(CS100) and BD-500-1A11 (CS300) airplanes and address it to:

Transport Airplane Directorate

Federal Aviation Administration

Attn. Stephen Happenny/ANM-112

1601 Lind Ave. SW

Renton, WA 98057

If we do not hear from you within 30 days, we will close the project without notifying you 

further. In the meantime, should you have any questions or concerns regarding this request,

please contact Stephen Happenny, ANM-112, at 425-227-2147, or e-mail, 

Stephen.Happenny@faa.gov.

Sincerely, 

Victor Wicklund

Manager, Propulsion & Mechanical Systems Branch

Transport Airplane Directorate, Aircraft Certification Service