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November 9th, 2012 

AW-BD5/12/760 

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) – 

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) Title 14 Code of Federal Regulations (14CFR) § 11.81, titled “What 

information must I include in my petition for an exemption?”, Docket No. 

1999–6622, 65 FR 50863, dated 2000-08-21. 

(3) FAA Memo PS-ANM-03-112-16, “Interim Policy on High Altitude Cabin 

Decompression (Reference Amendment 25-87)”, Federal Register Doc. 03-

13541, dated 2006-03-24. 

(4) Aviation Rulemaking Advisory Committee (ARAC) Transport Airplane 

Engine Issues Group (TAEIG) Mechanical Systems Harmonization Working 

Group (MSHWG), “Final Report on 14CFR 25.841(a)(2) and (3)”, dated 

2003-07-31, submitted to the FAA on 2003-10-21. 

(5) Aviation Rulemaking Advisory Committee (ARAC) Transport Airplane 

Engine Issues Group (TAEIG) Meeting, held 2003-10-15. 

 

Dear Mr. Napoleon, 

Further to a similar petition for exemption submitted to TCCA [see reference (1)], Bombardier 

Aerospace (BA) respectfully submits to the FAA this petition for exemption of the CSeries 

aeroplane models BD-500-1A10 & 1-A11 from the requirements of 14CFR § 25.841 (a)(2)(i) 

and (a)(2)(ii) at Amdt 25-87, with respect to Uncontained Engine Failures. This petition for 

Exemption is made in accordance with 14CFR § 11.81 [see reference (2)], is in line with the 

applicable FAA policy memorandum [see reference (3)], and is based on the Mechanical 

Systems Harmonization Working Group (MSHWG) report [see reference (4)] which was 

accepted by the Transport Airplane and Engine Issues Group (TAEIG) [see reference (5)]. 

HEADQUARTERS 

BOMBARDIER AEROSPACE 

400 CÔTE-VERTU ROAD WEST 

DORVAL, QUÉBEC CANADA H4S 1Y9 

TEL. 514-855-5000 

FAX. 514-855-7401 

www.bombardier.com
Page 2 of 2 

Enclosed with this letter is the Exemption Request Form which has been completed in 

accordance with 14CFR § 11.81. 

Should you require additional information, please contact Hagop Kazarian at (514) 855-5000 

x59083 or hagop.kazarian@aero.bombardier.com. 

Yours truly, 

Keith Barnett 

Airworthiness Manager, CSeries 

Bombardier Aerospace
Bombardier Airworthiness Coordination Sheet

Page 1 of 2 

Subject: BA letter AW-BD5/12/760, titled “CSeries airplane models BD-500-1A10 

(CS100) & BD-500-1A11 (CS300) – Petition for Exemption per 14CFR § 

11.61(b) from 14CFR § 25.841(a)(2) with respect to Uncontained Engine 

Failures”, dated 2012-11-09. 

Reference(s): 1. Airworthiness – CSeries Certification eRoom Action Item #2545. 

DISCIPLINE NAME APPROVAL / DATE 

Airworthiness Focal H. Kazarian 

Airworthiness Manager K. Barnett 
EXEMPTION REQUEST FORM

Page 1 of 1 

REQUEST MADE BY:

Bombardier Inc. 

400 Côte-Vertu Road West 

Dorval, Québec, Canada H4S 1Y9 

Contact Person: Keith Barnett 

Email: keith.barnett@aero.bombardier.com 

Tel: (514) 855-7567 

Fax: (514) 855-7301 

REQUEST MADE TO:

Federal Aviation Administration (FAA) 

New York Aircraft Certification Office (NYACO) 

14CFR PROVISION:

14CFR § 11.61(b) 

SPECIFIC SECTIONS OF 14CFR FROM WHICH WE SEEK AN EXEMPTION:

14CFR § 25.841(a)(2)(i) and (a)(2)(ii) 

We would also request the permission to exercise the privileges of this exemption outside the 

United States, most notably since the CSeries will operate internationally, and the basic design 

requirements, and any exemptions therefrom, should therefore be applicable worldwide, 

notwithstanding any additional foreign authority requirements that might also be applicable. 

THE EXTENT OF RELIEF WE SEEK:

14CFR § 25.841(a)(2) at Amendment 25-871

 requires that the cabin altitude does not exceed the 

limits specified in the sub-parts following various failures conditions, and 14CFR § 25.841(a)(3) 

at Amendment 25-87 further requires additional considerations for an uncontained engine failure 

(UEF) which punctures and/or tears the fuselage creating a very large hole (bigger than the 

critical hole size). 

The Bombardier Aerospace (BA) CSeries aeroplane models BD-500-1A10 & BD-500-1A11 are 

designed to cruise at a maximum altitude of 41,000 ft pressure altitude. Should an UEF occur at 

the maximum cruising altitude, it is possible that the cabin pressure could exceed the limits 

contained in current regulations since the fuselage hole size generated by the engine debris will 

exceed the allowable cabin altitudes, making it non-compliant to the above-mentioned 

certification requirements. 

 

1

Amendment 25-87 Final Rule, Docket 26070, Federal Register Volume 61, Number 109, June 5th, 1996. 
EXEMPTION REQUEST FORM 

Page 2 of 2 

THE REASON WE SEEK RELIEF:

Other airplane manufacturers have had similar difficulties meeting this certification requirement. 

In fact, no aircraft designs which incorporate a wing mounted engine lay-out have been certified 

to fully comply with this certification requirement and each manufacturer of such designs has 

elected to request an Exemption for aeroplanes where Special Conditions -Airworthiness – or the 

equivalent to 14CFR § 25.841(a) at Amendment 25-87 – have been in the basis of 

certification.2,3,4

EASA CS-25 is not harmonized with the AWM and 14CFR, and has allowed large airplanes to 

operate above 40,000 ft without requiring a similar request for Exemption.5

Furthermore, Industry data is available to support the number of engine rotor burst incidents and 

the resulting cabin decompressions in other manufacturer’s petitions for Exemptions.2,3,4

BA requests an exemption from compliance with 14CFR § 25.841(a)(2)(i) and (ii) for cabin 

depressurization that can occur from UEFs that result in large fragment penetration causing a 

very large hole in the fuselage. BA notes that the FAA Interim Policy6

 allows Exemptions from 

14CFR § 25.841(a) regarding the worst-case failures caused by an UEF, provided alternate 

criteria (time limits) can be met, and additional mitigating factors are present in the design of the 

airplane. 

The CSeries design will meet the requirements of 14CFR § 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 14CFR § 25.841(a)(2)(i) and (ii). Therefore, BA requests the 

exemption be granted for altitudes up to the CSeries maximum cruise altitude of 41,000 ft. A 

grant of exemption from this regulation would allow the CSeries to operate up to 41,000 ft, 

which could briefly expose cabin occupants to this altitude in the event of a worst-case 

decompression. 

Specifically, BA requests relief from 14CFR § 25.841(a)(2)(ii) which specifies that cabin 

pressure altitude may not exceed 40,000 ft for any duration after decompression from any failure 

condition not shown to be extremely improbable. A grant of exemption from this regulation 

would allow the CSeries cabin pressure altitude to exceed 40,000 ft following a decompression 

due to an UEF causing a very large hole in the fuselage. 

 

2

 FAA Exemption No. 8160 for the Embraer E170. Available online at

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgEX.nsf/0/cae639b1350ae04586256dce006727a6/$FILE/8160.pdf. 3

 FAA Exemption No. 8857 for the Boeing B787-8. Available online at 

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgEX.nsf/0/ee62f9861e47dee9862572b90052aaef/$FILE/8857.pdf. 4

 FAA Exemption No. 8695A for the Airbus A380. Available online at 

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgEX.nsf/0/26b96ca49ea7c03c862573db005abc08/$FILE/8695A.pdf. 5

 EASA, “Book 1 – Airworthiness Code”, Certification Specifications for Large Aeroplanes CS-25, Amendment 7, 

Annex to ED Decision 2009/013/R, October 21st, 2009. Available online at http://www.easa.europa.eu/agencymeasures/certification-specifications.php#CS-25. 6

 FAA Memo (HAPPENY, Steve), ANM-03-112-16 “Interim Policy on High Altitude Cabin Decompression 

(Reference Amendment 25-87)”, Federal Register Doc. 03- 13541, March 24th, 2006. 
EXEMPTION REQUEST FORM 

Page 3 of 3 

BA also requests relief from 14CFR § 25.841(a)(2)(i) which specifies that cabin pressure altitude 

may not exceed 25,000 ft for more than 2 minutes after decompression from any failure 

condition not shown to be extremely improbable. A grant of exemption from this regulation 

would allow the CSeries to take longer than 2 minutes to descend from 41,000 ft to 25,000 ft 

following a decompression due to an UEF causing a very large hole in the fuselage. 

Technical Information in Support of the Petition for Exemption:

BA offers the following justification in support of its petition for exemption (some of this 

justification is based on cabin decompression evaluations performed and reported by the 

Mechanical Systems Harmonization Working Group (MSHWG) under the auspices of the 

Aviation Rulemaking Advisory Committee (ARAC)7,8): 

1. The rule as written will force the CSeries to have an altitude limitation imposed which will 

be less than the 41,000 ft altitude being sought. The lay-out of the CSeries is conventional 

and thus is no less safe than other manufacturer’s aircraft which were certified prior to 

14CFR amendment 25-87 and operated above 40,000 ft. Furthermore, BA submits that the 

current rule and its associated limitations are not in the public’s best interest, since 

compliance with the current requirements may limit airplanes to a maximum operating 

altitude of less than 40,000 ft, and there will be an economic impact because of the increased 

fuel use and longer routes due to more congested airspace at lower altitudes, thus making the 

aircraft less attractive for potential sales. 

The CSeries is designed to fly at cruise altitudes that will maximize fuel efficiency. The 

reduction in maximum cruise altitude resulting from compliance with 14CFR § 25.841(a)(2) 

for UEF is a concern shared by other manufacturers of airplanes with wing-mounted engines 

seeking new or amended Type certification. No transport category airplane with wingmounted engines certificated today for operation above 39,000 ft can meet the new cabin 

altitude limits within the current 14CFR § 25.841(a)(2) without an exemption. 

2. In addition, BA observes that neither the Joint Airworthiness Authorities nor the European 

Aviation Safety Administration has implemented similar restrictions in their certification 

requirements.5

 

7

 Aviation Rulemaking Advisory Committee (ARAC) Transport Airplane Engine Issues Group (TAEIG). 

Mechanical Systems Harmonization Working Group (MSHWG), Final Report on 14CFR 25.841(a)(2) and (3), 

dated August 2003, submitted to FAA on October 21st, 2003. Available online at 

http://www.faa.gov/avr/arm/arac/aractasks/tae_mshwg3.doc. 

Note: This final report was approved by a majority of the members of ARAC: seven members of TAEIG voted to 

submit the report as a recommendation to the FAA, two members voted against submitting the report, and one 

member abstained. 

8

 Aviation Rulemaking Advisory Committee (ARAC) Transport Airplane Engine Issues Group (TAEIG) Meeting, 

held 2003-10-15. Minutes available online at 

http://www.faa.gov/avr/arm/arac/aracmin/oct_15_16_2003/meeting_minutes.doc. 
EXEMPTION REQUEST FORM 

Page 4 of 4 

3. The CSeries complies with the latest Canadian, US, and European requirements and therefore 

offers a significantly higher basic level of safety than previously certified transport category 

aircraft. 

4. UEFs are rare events, and UEFs causing rapid depressurization are even rarer.

BA believes, based on fleet service experience, that UEFs are rare events.9

 Modern transport 

category aircraft have a 45 year safety record with millions of hours and more than 30 years 

at altitudes similar to the maximum cruise altitude proposed for the CSeries. 

Data from previous accidents involving UEFs were compiled from many different sources: 

4.1. BA’s internal computerized Air Safety, Continuning Airworthiness, and FRACAS 

databases. 

4.2. Canadian Transportation Safety Board (TSB) accident reports. 

4.3. US National Transportation Safety Board (NTSB) accident reports, special reports, and 

computerized databases. 

4.4. Society of Automotive Engineers (SAE) Accident Investigation Reports (AIR): 

4.5. British Department of Transport Air Accidents Investigation Branch (AAIB) accident 

reports. 

4.6. US FAA’s online Lessons Learned from Transport Airplane Accidents database10. 

4.7. Communications with safety representatives of major aircraft manufacturers, including 

reports and data they have provided11. 

4.8. Communications with safety representatives of major engine manufacturers, including 

reports and data they have provided. 

4.9. Previous similar exemption requests. 

In 1974, the NTSB published a special study12 of turbine engine rotor disk failures from 1962 

to 1973,” which presents data on 41 cases of engine disk failures in public transport aircraft. 

This was primarily focused on low bypass engines, but did include six (6) 1st generation high 

bypass engine events. The NTSB safety recommendations focused on a goal of disk 

containment. The NTSB database covers the years 1962 to present containing all the 

information on the accident report from NTSB 6120.4 or its predecessor. The files contain 

additional information not published in the cause report. 

Society of Automotive Engineers (SAE) Investigation Reports (AIR) titled “Report on 

Aircraft Engine Containment” provide the most concise information on the causes of such 

 

9

 According to SAE AIR4770, the probability of an UEF is ~1.6x10-7 per flight hour for the world fleet. 10 FAA Lessons Learned From Transport Airplane Accidents database, available online at: http://accidentsll.faa.gov/ll_main.cfm?TabID=3&CategoryID=12

11 Boeing Commercial Airplanes, “Statistical Summary of Commercial Jet Airplane Accidents, Worldwide 

Operations, 1959-2002”, May 2003. 

Boeing Commercial Airplanes, “Statistical Summary of Commercial Jet Airplane Accidents, Worldwide Operations, 

1959-2003”, May 2004. 12 NTSB, NTSB-AAS-74-4 – Special Study - Turbine Engine Rotor Disk failures, Published 1974. 
EXEMPTION REQUEST FORM 

Page 5 of 5 

failures and are invaluable in predicting the occurrence rate of UEFs: 

4.10. SAE AIR 153713, covering the period of 1962 through 1975. 

4.11. SAE AIR 400314, covering the period of 1976 through 1983. 

4.12. A third report, SAE AIR 477015, covering the period of 1984 through 1989, was 

prepared but never published. 

These reports focused on the location of the failure (turbine, fan, compressor, etc.), the flight 

stage at failure (takeoff, climb, cruise, etc.), and when determinable, the cause of the failure 

(fatigue, material defect, etc.), for the entire commercial transport fleet. They contain limited 

data on airplane effects, and do not address the development of events after failures leading 

to catastrophic loss of the aircraft. 

Delucia, Salvino, Fenton et al produced a series of statistical reports on “Aircraft Gas 

Turbine Engine Rotor Failures” covering US commercial aviation in the late 1980s. The 

reports’ definition of “rotor failure” encompassed many kinds of turbomachinery failures, 

and the reports are therefore less specific. 

The SAE AIR reports provide enough data to estimate the probability of UEFs using fault 

tree analysis (FTA). An alternate method is failure modes and effect analyses (FMEA), but 

FTA is found to be a more suitable method according to section 2.2. of the 1997 FAA 

DOT/FAA/AR-96/95 report on UEF debris16. 

Although it is considered difficult to quantify precisely using 2nd generation data (the 

CSeries uses 3rd generation engines), the CSeries UEF rate can be conservatively assessed 

to be on the order of < 1×10-7 per engine hour. 

The CSeries has: 2 engines, and the probability of an UEF event at cruise is 14% (FAA 

AC20-128), therefore the CSeries UEF rate at high altitude = 2 × 0.14 × 1×10-7 = 2.8×10-8

per aircraft hour. 

Even considering the subsequent probability that the uncontained debris strikes the fuselage 

and creates a large hole causing a rapid cabin depressurization (generally approximated using 

a 0.1 multiplier,), BA and other engine and airplane manufacturers still can not declare that 

the event is less than 1×10-9 certification requirement, as such cases are potentially 

catastrophic. However such cases are approaching extremely improbable and that the design 

is what is technologically practical for wing-mounted engine airplanes. 

Notwithstanding the above, the CSeries uses state-of-the-art 3rd generation Pratt & Whitney 

PurePower® PW1500G series Geared TurbofanTM (GTF) engines which incorporate 

 

13 SAE AIR 1537, Report on Aircraft Engine Containment: 1962 to 1975, dated 1977. 14 SAE AIR 4003, Report on Aircraft Engine Containment: 1976 to 1983, dated 1987. 15 SAE AIR 4770 Draft, Report on Aircraft Engine Containment: 1984 to 1989, dated 1994. 16 FAA DOT/FAA/AR-96/95, Final Report: The Potential for Fuel Tank Fire and Hydrodynamic Ram From 

Uncontained Aircraft Engine Debris, dated January 1997. 
EXEMPTION REQUEST FORM 

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improvements in engine technology (e.g. enhanced vibration/trend monitoring) and state-ofthe art 3rd generation engine design practices which apply lessons learned with respect to 

UEFs, all of which can be expect to further increase the reliability and decrease the risk of 

UEFs for the CSeries family of airplanes. 

Furthermore, BA will provide TCCA with calculation of the probability for the CSeries of an 

UEF during cruise causing a large hole in the fuselage and leading to rapid depressurization. 

BA believes the likelihood for the CSeries is lower than similar previously certificated 

transport category airplane with wing-mounted engines. 

5. Rapid depressurization events rarely result in risk to occupants: 

BA notes that very few, if any, rapid depressurization events have exposed an airplane cabin 

to pressure altitude profiles which pose a risk of injury to occupants. Industry history reveals 

that few cases of catastrophic decompressions at high altitude have occurred (see 4 above for 

those a summary of those caused by a UEF), and those that have occurred have typically 

involved small business jets. BA observes that the FAA has cited a few cases of UEFs in 

cruise10,17. In one such instance, the crew of a DC-10 crossing New Mexico reported several 

cases of initial decompression sickness, apparently with no permanent injuries18. However, 

the UEF in that case was believed to have been induced by crew action. 

Furthermore, the MSHWG report7

 concluded for the world commercial jet fleet for the 

period of 1992 to 2001, that none of the known depressurization events have resulted in 

severe cases of occupant hypoxia.

6. Aerospace hypoxia physiology data shows no difference between 40,000 feet or 41,000 feet:

Several research papers have been circulated in the aerospace medical community generating 

controversy regarding the absolute physiological limits to occupants following cabin 

depressurization. However, the consensus is that the physiological limits are not significantly 

affected if cabin depressurization occurs at 40,000 feet or 41,000 feet. 

The FAA and other qualified experts agree that the severity of hypoxia exposure to rapid 

depressurization is determined by the pressure field and duration of the event. This is 

predicated on observations made from flight physiological and medical experiments. The 

cabin altitude limits in Amendment 25-87 were developed by the FAA based in part on 

recommendations from the FAA’s Civil Aeromedical Institute (CAMI), which were based on 

the concept of “Time of Safe Unconsciousness” (TSU) documented by James G. Gaume in 

his 1970 paper. The study concluded with the statement that, “[...] a plea must be made for 

collection of better data” 19. Gaume’s 1970 paper is only one source in establishing adequate 

safety basis. It should be understood that the proposed TSU criteria was established as a 

compensating consideration to the elimination of the passenger oxygen system. Today’s 

 

17 Uncontained Engine Damage Database, ACCESS 2000 Database, FAA UED v001, June 10th, 2002. 18 NTSB-AAR-75-2, Aircraft Accident, National Airlines Inc., DC-10, N60NA near Albuquerque, New Mexico, 

November 3rd, 1973. 

19 GAUME, James G., “Factors influencing the Time of Safe Unconsciousness (TSU) for commercial passengers 

Following Cabin Decompression”, Aerospace Medicine, April 1970, 382-385. 
EXEMPTION REQUEST FORM 

Page 7 of 7 

commercial transport are required to provide an emergency oxygen system providing 

additional margin of safety. The MSHWG agreed additional data based on further study 

would benefit the establishment of new standards. In lieu of new data, the MSHWG 

established physiological exposure limits that are conservative with respect to the data 

available. The MSHWG considered the available physiological exposure research which 

included several papers that have been circulated in the aerospace medical community, all 

with the objective of establishing physiological limits to occupants following cabin 

decompression. It was based on these papers, and consideration of the overall risk to 

decompression exposure that the MSHWG documented its recommendations in the TAEIG 

accepted report7. The following are summaries of the reports from recognized Aerospace 

Medical Doctors addressing physiological information that was considered by the MSHWG: 

6.1. James G. Gaume (Aerospace Medicine) authored a paper substantiating the new rule. 

According to Gaume, during an emergency descent from 42,000 ft to 5,000 ft for 

adequate recovery of unconscious passengers without any supplemental emergency 

oxygen to the occupants, with an aircraft emergency descent of 6,200 ft per minute and 

with cabin altitude exceeding 33,000 ft, no more than 1 minute and 42 seconds is 

considered acceptable.19

6.2. Dr. Stanley R. Mohler, a former director of the FAA’s CAMI, analyzed a number of 

actual depressurization cases, including data from studies by Barron20, and Gaume19. He 

concluded that brain damage in the absence of oxygen starts after about four minutes, 

and that three minutes above 25,000 ft is a reasonable limit to protect against permanent 

physiological damage from a cabin depressurization occurring at up to 45,000 ft.21

6.3. Dr. Robert Garner, Research Physiologist, Protection and Survival Laboratory at the 

FAA’s CAMI, agrees that limiting cabin altitude exposure to 25,000 ft for up to three 

minutes and never allowing it to exceed 45,000 ft would provide an acceptable level of 

safety. His views on this matter have been communicated to the FAA Transport 

Standards Staff. 

6.4. Draft White paper issued by the FAA’s CAMI - FAA Civil Aerospace Medical Altitude 

Rule: presented in the MSHWG in July 2002, states that exposure: if unprotected, 

passengers to a 41,000 ft altitude would be approximately equal to exposure at a 40,000 

ft altitude. 22

6.5. J.B. Brierley and A. N. Nicholson concluded in a 1969 study that cabin altitude 

exposure above 10,000 ft not more than eight minutes up to peak of 36,000 ft does not 

cause brain damage.23

6.6. A. N. Nicholson and J.R. Ernsting concluded in a 1967 study that cabin altitude 

exposure above 40,000 ft with time exposure of 1 minute and 30 seconds caused brain 

damage.24 

 

20 BARRON, C. and COOK, T., “Effects of Variable Decompressions to 45,000 feet”, Aerospace Medicine, May 

1965, 425-430. 

21 MOHLER, Dr. Stanley, “Sudden High Altitude Cabin Decompression Immediately Threatens Safety of Aircraft 

Crew and Passengers”, Flight Safety Foundation, Human Factors & Aviation Medicine, December 1994. 22 CAMI & FAA, “Draft White paper on Civil Aerospace Medical Altitude Rule”, presented in the MSHWG in July 

2002, p.13. 

23 BRIERLEY, J.B. and NICHOLSON, A.N., “Neurological Study of Simulated Decompression in Supersonic 

Transport Aircraft”, Aerospace Medicine, August 1969. 
EXEMPTION REQUEST FORM 

Page 8 of 8 

In consideration of the above studies, comments received on the FAA Interim Policy6

, and the 

acceptance of the MSHWG report7 by TAEIG, the FAA established appropriate criteria for 

14CFR § 25.841(a) with respect to an UEF. These criteria are more conservative than those 

established by the MSHWG report. In lieu of any other standard, BA will comply with these 

criteria as presented in the Proposed Conditions by Party Making the Request, to Show How the 

Exemption Would Provide a Level of Safety At Least Equal to the Existing Rule: section, which 

need to be confirmed by the FAA as appropriate.

HOW OUR REQUEST WOULD BENEFIT THE PUBLIC AS A WHOLE:

Permitting the CSeries to fly above 40,000 ft does offer real and tangible benefits to the 

aerospace industry, the traveling public, and the economy, and is therefore in the public interest: 

a) Lower air traffic management costs. 

Three separate studies have shown that the number of operations above 37,000 ft are 

significant today and the trend is for newer airplanes to cruise at these altitudes for even 

longer portions of their mission. Limiting operation of new generation airplanes to lower 

altitudes will result in higher traffic density, which in turn will result in higher cost of safety 

in order to maintain established air traffic vertical and horizontal separation requirements, 

which is not in the public interest. Conversely, the cost of maintaining the level of safety 

within the existing air traffic management system will not be adversely impacted by 

continuing to allow operation in the less congested altitudes, typically well above 37,000 ft. 

b) Better fuel economy and lower operating costs. 

The CSeries uses state-of-the-art 3rd generation Pratt & Whitney PurePower® PW1500G

series Geared TurbofanTM (GTF) engines which have been designed to offer double-digit 

improvements in fuel burn at higher altitudes, and associated lower operating costs. In fact, 

initial fuel burn improvements — gate-to-gate — have been estimated at 16% versus today’s 

best 2nd generation turbofan engines. With the benefits of a new, advanced airplane such as 

the CSeries, the fuel burn benefit can be even greater — over 20% versus today’s best 

aircraft. That can be a significant savings to airlines and airline passengers. Therefore, 

granting this exemption is clearly in the interest of the public since it allows the CSeries to 

operate on routes and generate significantly lower emissions and noise than other aircraft 

types that are currently operating on those same routes. 

Furthermore, limiting CSeries operations to lower than 40,000 ft will result in significantly 

increased fuel burn since operations at lower altitudes in certain environmental conditions are 

not optimum for these aeroplanes and engines. Since additional fuel is required for an 

otherwise identical route, this ultimately increases CSeries operating costs, which is clearly 

not in the interest of airlines and airline passengers. 

 24 NICHOLSON, A.N. and ERNSTING, J.R., “Neurological Sequelae of Prolonged Decompression”, Aerospace 

Medicine, April 1967. 
EXEMPTION REQUEST FORM 

Page 9 of 9 

c) Lowering noise and emissions. 

The CSeries uses state-of-the-art 3rd generation Pratt & Whitney PurePower® PW1500G

series Geared TurbofanTM (GTF) engines which have been designed to offer double-digit 

improvements in environmental emissions (e.g. CO2, NOx) and noise when compared to 

current 2nd generation turbo-fan engines. In fact, the use of those engines on the CSeries cuts 

carbon emissions by over 3,000 metric tonnes — equal to planting over 700,000 trees — per 

aircraft per year, and slashes aircraft noise footprints by up to 75% — a big relief to 

communities. At up to 20 decibels below today’s most stringent standard, it is the quietest 

engine in its class: meaning lower noise fees, shorter flight tracks, extended curfew 

operation, and quieter cabins: this is clearly in the interest of airlines and passengers. In 

addition, Pratt & Whitney’s TALONTM X combustor slashes NOx exhaust gases 50% below 

CAEP/6. Since preserving a clean atmosphere, reducing green house gas emissions, and 

lowering community noise is in everyone’s best interest, granting this exemption is clearly in 

the interest of the public since it allows the CSeries to operate on routes and generate 

significantly lower emissions and noise than other aircraft types that are currently operating 

on those same routes. 

d) Fostering a competitive aviation industry. 

A reduction in maximum cruise altitude would also adversely impact the ability of the 

CSeries to compete with previously certificated airplanes which can operate at the more 

economical cruise altitudes typically in excess of 37,000 ft. If compliance with 14CFR § 

25.841(a) limited airplanes operations to a maximum altitude of 40,000 ft, this would impose 

a significant disadvantage on newly designed airplanes that have many safety advantages 

over older airplanes currently allowed to operate at higher altitudes. This would delay the 

introduction of these airplanes and the benefits of their more advanced technology. 

Therefore, denial of this petition would deny the public some of the benefits of a new family 

of airplanes. The CSeries family of airplanes will incorporate new technology, lessons 

learned from previous and current production airplanes, and comply with the latest 

airworthiness standards throughout to provide a safer, more efficient transportation option for 

airlines and airline passengers. 

e) Lower cost of air travel for the public. 

The CSeries will provide industry-leading operating economics, and environmental 

improvements. Granting this petition of exemption is in the public interest because it will 

improve safety relative to previously certificated airplanes, while reducing noise, emissions, 

operational costs (fuel burn due to better engines, air traffic management service fees for 

airlines due to less crowded airspace), and ultimately making air transport more accessible, 

more efficient, and less costly for the travelling public. 

These benefits will accrue with no decrease in safety. 

REASONS WHY THE EXEMPTION WOULD NOT ADVERSELY AFFECT SAFETY:

Permitting the CSeries to fly above 40,000 ft does not adversely affect aviation safety. 
EXEMPTION REQUEST FORM 

Page 10 of 10 

a) Since the release of Amendment 25-87, a number of amendments to 14 CFR 25 have been 

released. Each of these amendments has the intent of increasing aviation safety. The CSeries 

will meet the latest amendments in effect at the time of application and therefore offers a 

higher level of safety than do previously certificated transport category airplanes. The net 

result is that the CSeries incorporates all the safety advancements as intended within these 

later amendments. Any significant impact to the marketability of the CSeries will, at a 

minimum, result in a reduced number of aircraft with this higher level of safety as compared 

with the previous generation of aircraft, or at a maximum, preclude the manufacture of this 

new generation of aircraft, which adversely affects global aviation safety. 

b) The CSeries fully complies with the latest airworthiness standards including 14CFR § 25.841 

(a)(2) and (3) in all regards, except as related to an UEF as defined herein. Specific features 

have been incorporated into the CSeries design to mitigate the safety risk to occupants due to 

a decompression resulting from an UEF. Improvements in engine technology, application of 

lessons learned, and 3rd generation engine design practices have resulted in a reduction in 

UEF events and the risk of a rapid depressurization. 

c) Restricting airplane operations to lower altitudes will increase traffic congestion at the 

detriment of aviation safety. Since higher traffic densities result in higher air traffic controller 

and pilot workloads, which in turn increase the risk of accidents, the granting of this 

exemption provides for increased aviation safety from an air traffic management standpoint. 

d) 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 and other design 

features. As concluded herein, and based on the MSHWG report7

, the world commercial jet 

fleet has had no hypoxia related fatalities due to in-flight decompression events caused by an 

UEF. This safety record has been maintained even as newer airplanes fly at higher altitudes 

more often than older airplanes. In keeping with time-above-altitude FAA guidance and the 

recommendations of the MSHWG report7

, BA has incorporated design features that 

appropriately address the risk to safety following an UEF. Therefore, granting of the 

exemption will not compromise safety to the airplane occupants. 

PROPOSED CONDITIONS BY PARTY MAKING THE REQUEST, TO SHOW HOW

THE EXEMPTION WOULD PROVIDE A LEVEL OF SAFETY AT LEAST EQUAL TO 

THE EXISTING RULE:

BA believes that although 14CFR § 25.841(a)(2) and (3) intend to mitigate certain risks to 

safety, they also create unintended consequences. The existing word-wide fleet of transport 

category aeroplanes has demonstrated safe operations during millions of hours of flight at 

altitudes similar to or higher than those proposed for the CSeries. Therefore, as outlined in the 

FAA Interim Policy6, the risk of rapid depressurization following an UEF is better mitigated by a 

combination of proven design practices established through years of airplane industry experience 

combined with today’s improved technical capabilities. It is intended that the following proposed 
EXEMPTION REQUEST FORM 

Page 11 of 11 

risk mitigation measures augment this exemption request and address the intended concern for 

safety without the non-commensurate impacts driven by current requirements of 14CFR § 

25.841(a)(2). 

a) It must be reiterated that this request for exemption from compliance to 14CFR § 

25.841(a)(2) is limited to UEFs, and the CSeries will fully comply with the latest 

airworthiness standards including 14CFR § 25.841(a)(2) and (3) for other sources of rapid 

depressurization, including system failures and specific structural failures, except as related 

to an UEF. All mechanical and/or functional interfaces that could potentially violate the 

physiological limits imposed by 14CFR § 25.841(a) are considered. Robust structural and 

systems design and the ability for the airplane to rapidly descend are key to assuring the 

safety of airplane occupants and are an inherent part of the CSeries design. BA design 

practices refine the requirements into sub-requirements for systems, structures, 

aerodynamics, and performance in order to assure airplane level compliance (for example, it 

is still our overall design objective to descend below 25,000 ft in under 2 minutes for UEF 

cases). Furthermore, the CSeries design ensures separation and redundancy of key systems 

that are required for the emergency descent, such as electrical power, flight crew and 

passenger oxygen, cabin pressure control, and spoiler actuation. 

b) The Airplane Flight Manual (AFM) will clearly state that the CSeries is limited to operate up 

to 41,000 ft pressure altitude, and will include appropriate procedures for emergency descent 

following loss of cabin altitude or an engine failure. 

c) Other threat minimization philosophies employed on the CSeries include 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). 

d) In consideration of the above studies and the acceptance of the MSHWG report7

 by TAEIG, 

the FAA established appropriate criteria for 14CFR § 25.841(a) with respect to an UEF in its 

Interim Policy6. BA notes that these criteria are more conservative than those established by 

MSHWG report7

. Therefore, in lieu of any other standard, BA will comply with the 

following alternate criteria to be considered for the UEF case only: 

Criteria for rapid decompression following an UEF:

The airplane must be designed so that occupants will not be exposed to a cabin 

pressure altitude that exceeds the following after decompression from any engine 

failure condition not shown to be extremely improbable: 

(i) Forty-five thousand (45,000) feet for any duration; or 

(ii) Forty thousand (40,000) feet for one minute; or 

(iii) Twenty-five thousand (25,000) feet for more than three minutes; or 

(iv) Ten thousand (10,000) feet for more than six minutes. 

e) In calculating the descent capability of the aeroplane in order to meet the revised cabin 

altitude conditions in d), pilot recognition and reaction time will be considered. There is a 
EXEMPTION REQUEST FORM 

Page 12 of 12 

consensus in the MSHWG that a value of 17 seconds is the acceptable value to recognize the 

failure and initiate descent. 

f) In calculating the descent capability of the aeroplane in order to meet the revised cabin 

altitude conditions in d), the loss of the failed engine’s contribution as a source of power to 

the systems enabling 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 debris damage from the actual UEF (e.g. 

hydraulic line rupture, wiring damage, etc...) will not be considered. 

g) In calculating the descent capability of the aeroplane in order to meet the revised cabin 

altitude conditions in d), various dispatch conditions will also be considered. 

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. This 

feature will be shown to comply with all applicable certification requirements, however the 

CSeries will fully comply with the latest airworthiness standards including AWM 

525.841(a)(2) and (3) for rapid depressurization without taking certification credit for this 

feature. 

SUMMARY THAT CAN BE PUBLISHED IN THE FEDERAL REGISTER:

14CFR § 25.841(a)(2) at Amendment 25-87 requires that the cabin altitude for commercial 

airplanes not exceed the limits specified in the sub-parts following various failures conditions, 

and 14CFR § 25.841(a)(3) at Amendment 25-87 further requires additional considerations for an 

uncontained engine failure (UEF) which punctures and/or tears the fuselage creating a very large 

hole (bigger than the critical hole size). 

The Bombardier Aerospace (BA) CSeries aeroplane models BD-500-1A10 & BD-500-1A11 are 

designed to cruise at a maximum altitude of 41,000 ft pressure altitude. Should an UEF occur at 

the maximum cruising altitude and should the engine debris create a very large hole in the 

fuselage, it is possible that the cabin pressure could exceed the limits contained in current 

regulations, making it non-compliant to the above-mentioned certification requirements. 

Other airplane manufacturers have had similar difficulties meeting this certification requirement. 

In fact, no aircraft designs which incorporate a wing mounted engine lay-out have been certified 

to fully comply with this certification requirement and each manufacturer of such designs has 

elected to request an Exemption. Furthermore, EASA CS-25 is not harmonized with the AWM 

and 14CFR, and has allowed large airplanes to operate above 40,000 ft without requiring a 

similar request for Exemption: therefore, airplanes built and operated in Europe have not had to 

consider similar requirements for UEFs. 
EXEMPTION REQUEST FORM 

Page 13 of 13 

BA requests an exemption from compliance with 14CFR § 25.841(a)(2)(i) and (ii) for cabin 

depressurization that can occur from UEFs that result in large fragment penetration causing a 

very large hole in the fuselage. BA notes that the FAA Memo PS-ANM-03-112-16 

titled“Interim Policy on High Altitude Cabin Decompression (Reference Amendment 25-87)”

(Federal Register Doc. 03-13541, dated 2006-03-24) allows Exemptions from 14CFR § 

25.841(a) regarding the worst-case failures caused by an UEF, provided alternate criteria (time 

limits) can be met, and additional mitigating factors are present in the design of the airplane. 

BA submits that this petition for Exemption would benefit the public as a whole since it would 

lead to lower air traffic management costs, better fuel economy, lower operating costs, and lower 

noise and emissions, and consequently lead to lower cost of air travel for the public and therefore 

foster a competitive aviation industry. 

BA also submits that this petition for Exemption would not adversely affect safety since the 

CSeries fully complies with the latest airworthiness standards including 14CFR § 25.841 (a)(2) 

and (3) in all regards, except as related to an UEF as defined herein. 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). Improvements in engine technology, application of lessons learned, and 3rd

generation engine design practices have also resulted in a reduction in UEF events. In addition, 

the world commercial jet fleet has had no hypoxia related fatalities due to in-flight 

decompression events caused by an UEF, and this safety record has been maintained even as 

newer airplanes fly at higher altitudes more often than older airplanes. Since the CSeries will 

meet the latest amendments in effect at the time of application and therefore offers a higher level 

of overall safety than do previously certificated transport category airplanes, granting of the 

exemption will not compromise safety to the airplane occupants. Furthermore, BA notes that 

refusing this exemption and restricting airplane operations to lower altitudes will increase traffic 

congestion at the detriment of aviation safety: since higher traffic densities result in higher air 

traffic controller and pilot workloads, which in turn increase the risk of accidents, the granting of 

this exemption provides for increased aviation safety from an air traffic management standpoint.