### Exemption No. 10944

UNITED STATES OF AMERICA DEPARTMENT OF TRANSPORTATION FEDERAL AVIATION ADMINISTRATION RENTON, WASHINGTON 98057-3356

ln the matter ofthe petition of 

### Bombardier Aerospace Company for an exemption from 

### § 25.841(a)(2) ofTitle 14, Code ofFederal Regulations 

### Regulatory Docket No. 

### FAA-2012-1146

PARTIAL GRANT OF EXEMPTION

By letter no. AW-BD5112/760 received November 9, 2012, Mr. Keith Barnett, CSeries Airworthiness Manager, Bombardier Aerospace Company, 400 Cote-Vertu Road West, Dorval, Quebec, Canada H4S 1Y9, petitioned to exempt the CSeries Model BD-500-1A1 0 (CS 1 00) and BD-500-1A11 (CS300) airplanes from the requirements of§ 25.841(a)(2), at Amendment 25-87, ofTitle 14, Code ofFederal Regulations (14 CFR). An exemption would relieve these airplanes from the requirement that, during a decompression caused by a failure ofone ofthe engines, airplane cabin pressure altitude not exceed 25,000 feet for more than two minutes, or exceed 40,000 feet for any duration. In addition, the FAA received, on August 12, 2013, supplemental material proprietary to BombardierAerospace Company that addressed specific questions pertaining to their petition. This information was used in the FAA·s analysis for this exemption. 

### The petitioner requests relieffrom the following regulation: Section 25.84l(a)(2) at Amendment 25-87

- requires that 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 failure condition not shown to be extremely improbable: (i) Twenty-five thousand (25,000) feet for more than 2 minutes; or (ii) Forty thousand (40,000) feet for any duration

. 

### The petitioner supports their request with the following information: This section summarizes and quotes, with minor edits for clarity, the relevant information from the petitioner"s request. Their complete petition is available at the Department of Transportation's Federal Docket Management System, on the Internet at http://regulations.gov, in DocketNo

. FAA-2012-1146. The Bombardier Aerospace Company (BA) Model CSI00 and CS300 airplanes are designed to operate at a maximum cruise altitude of41 ,000 feet pressure altitude. Should an uncontainedengine-rotor burst (UEF) event occur, it is possible that the cabinpressure could exceed the limits contained in current regulations. BA offers the followingjustification in support ofits petition for exemption. Some ofthisjustification is based on cabin decompression evaluations performed and reported by the Mechanical Systems Harmonization Working Group (MSHWG) under the auspices ofthe Aviation Rulemaking Advisory Committee (ARAC) 1 in which Bombardier participated. Per BA'spetition: The CSeries design will meet the requirements of 14 CFR § 25.84l(a)(2)(i) and (ii) for all system and structural failures but not for all types ofengine 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). Therefore, BA requests the exemption be granted for altitudes up to the CSeries maximum cruise altitude of41 ,000 ft. A grant ofexemption from this regulation would allowthe CSeries to operate up to 41 ,000 ft, which could briefly expose cabin occupants to this altitude in the event ofa worst-case decompression

.

. ..the CSeries complies with the latest Canadian, US, and European requirements and therefore offers a significantly higher basic level ofsafety than previously certified transport category aircraft. Furthermore UEFs are rare events, and UEFs causing rapid depressurization are even rarer. BA believes, based onfleet service experience, that UEFs are rare events. BA points outthat modern transport-category airplanes have a 45-year safety record with millions offlight hours, and more than 30 years at altitudes similarto the maximum cruise altitude proposed for the CSeries. In addition, BA states that the European Aviation Safety Administration has not implemented similar restrictions. BA states that other airplane manufacturers have had similardifficulties meeting this certificationrequirement and that no airplane designs, which incorporate a wing-mounted engine configuration, have been certified to fully comply with this certification requirement (e.g., Airbus A380, Boeing 787-8, and EmbraerERJ-170). These manufacturers have elected to request an exemption when§ 25.84\(a), at Amendment 25-87, has been in the certification basis

. BA notes that very few, ifany, rapid depressurization events have exposed an airplane cabin to pressure altitude profiles that pose a risk ofinjury to occupants. Industry history reveals that few cases ofcatastrophic decompressions at high altitude have occurred, and those that have occurred have typically involved small businessjets. BA observes that the FAA has cited a few cases of UEFs in cruise. In one such instance, the crewofa DC-10 crossingNew Mexico reported several cases ofinitial decompression sickness, apparently with no permanent injuries. However, the UEF in that case was believed to have been induced by crew action. BA's petition fut1her states: Aerospace hypoxiaphysiology data shows no difference between40,000 feet or41,000 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 ifcabin depressurization occurs at 40,000 feet or41 ,000 feet.

1The Final Report ofthe MSHWG, dated August 2003, was approved by a majority ofthe members ofARAC's Transport Airplane Engine I ssues Group (TAEIG). Seven members ofTAEIG voted to submit the report as a recommendation to the FAA; two members voted against submitting the report, and one member abstained.

2BA adds that the Model CS100 and CS300 airplanes are designed to fly at cruise altitudes that will maximize fuel efficiency. A reduction in maximum cruise altitude resulting from compliance with § 25.841 (a)(2) for UEF is a concern shared by other manufacturers ofairplanes with wing-mounted engines seeking new or amended type certification. No transport-category airplane with wing-mounted engines certificated today, for operation above 39,000 feet, can meet the new cabin-pressure-altitude limits, within the current requirements of§ 25.841(a)(2), without an exemption. In addition, BA states that specific features have been incorporated into the CSeries airplane design to mitigate the safety risk to occupants due to a decompression resulting from an UEF. According to BA, the CSeries uses state-of-the-art, 3rd-generation, Pratt & Whitney PurePower® PW1500G series Geared TurbofanTM (GTF) engines that incorporate improvements in engine technology (e.g. enhanced vibration/trend monitoring) and state-of-the-art, 3rd-generation enginedesign practices that apply lessons learned with respect to UEFs, all ofwhich can be expect to further increase the reliability and decrease the risk ofUEFs for the CSeries airplanes. BA adds that restricting airplane operations to lower altitudes, to meet§ 25.841(a)(2) requirements, wiII increase traffic congestion. Limiting operation ofnew-generation airplanes to lower altitudes will result in highertraffic density that, in turn, will result in higher cost ofsafety to maintain established air-traffic vertical and horizontal separation requirements. BA confirms that the Model CS100 and CS300 airplanes will meetthe latest amendments in effect at the time ofapplication, except as noted within their certification basis. The net result is that the Model CS100 and CS300 airplanes incorporate all the safety advancements, as intended, within these later amendments. Any significant impact to the marketability ofthe Model CS100 and CS300 airplanes will, at a minimum, result in a reduced number ofairplanes with this higher level ofsafety, as compared with the previous generation ofairplanes, or at a maximum, preclude the manufacture ofthis new generation ofairplanes. In eithercase, Amendment 25-87 results in a reduced potential for overall aviation safety improvements. BA's petitioncontinues: Furthermore, the CSeries design ensures separation and redundancy ofkey systems that are required for the emergency descent, such as electrical power, flight crew and passenger oxygen, cabin pressure control, and spoiler actuation

... 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); The CSeries will have an Emergency Descent Mode (EDM) which will provide an additional margin ofsafety by initiating a descent automatically ifthere is no flight crew action following a loss ofcabin pressure orwhen 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 withouttaking certification credit for this feature. 

### Statement ofpublic interest 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:

3a) Three separate studies have shown that the number ofoperations above 37,000 ft are significanttoday and the trend is for newer airplanes to cruise at these altitudes for even longer portions oftheir mission. Limiting operation ofnew generation airplanes to lower altitudes will result in highertraffic density, which in turn will result in higher cost of safety in orderto maintain established air traffic vertical and horizontal separation requirements, which is not in the public interest. Conversely, the cost ofmaintaining the level ofsafety 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) 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 ofa 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, grantingthis exemption is clearly in the interest ofthe 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 lowerthan 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 ofairlines and airline passengers. c) The CSeries uses state-of-the-art 3rd generation Pratt & Whitney PurePowerPWISOOG series GTF engines which have been designed to offer double-digit improvements in environmental emissions (e.g. C02, NOx) and noise when compared to current 2nd generation turbo-fan engines. In fact, the use ofthose engines on the CSeries cuts carbon emissions by over 3,000 metric tonnes

- equal to planting over 700,000 trees- per aircraft peryear, and slashes aircraft noise footprints by up to 75%- a big reliefto communities. At up to 20 decibels belowtoday's most stringent standard, it is the quietest engine in its class: meaning lowernoise fees, shorter flight tracks, extended curfew operation, and quieter cabins: this is clearly in the interest ofairlines and passengers. In addition, Pratt & Whitney's TALON X combustor slashesNOx exhaust gases 50% below CAEP/6. Since preserving a clean atmosphere, reducing greenhouse gas emissions, and lowering community noise is in everyone's best interest, granting this exemption is clearly in the interest ofthe public since it allows the CSeries to operate on routes and generate significantly loweremissions and noise than other aircraft types that are currently operating on those same routes. d) A reduction in maximum cruise altitude would also adversely impact the ability ofthe CSeries to compete with previously certificated airplanes which can operate at the more economical cruise altitudes typically in excess of37,000 

### ft. Ifcompliance with 14CFR 

### § 25.84l(a) limited airplanes operations to a maximum altitude of40.000 ft, this would impose a significant disadvantage on newly designed airplanes that have many

4safety advantages over older airplanes currently allowed to operate at higher altitudes. This would delay the introduction ofthese airplanes and the benefits oftheir more advanced technology. Therefore, denial ofthis petition would deny the public some of the benefits ofa new family ofairplanes. The CSeries family ofairplanes will incorporate new technology, lessons learned from previous and current production airplanes, and comply with the latest airwm1hiness standards throughout to provide a safer, more efficient transportation option for airlines and airline passengers. e) The CSeries will provide industry-leading operating economics, and environmental improvements. Granting this petition ofexemption 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. 

### Federal Register publication A summary ofthe petition was published in the Federal Register on May 28, 2014 [79 FR 30684]. No comments were received. 

### The FAA's analysis Bombardier Aerospace Company provided the following information to support its petition for exemption fi·om § 25.841(a)(2)(i) and (ii):

• a background ofthe current rule and recent activities to harmonize it;

• a review ofthe safety history ofhigh-altitude commercial flight;

• a discussion ofhypoxia-physiology dataupon which recent rulemaking activities are based;

• a discussion ofthe impact ofcompliance with uncontained engine-rotor-burst aspects of the existing rule;

• environmental and air-traffic considerations; and,

• statements addressing public interest and no adverse impact to safety In response to FAA inquiries, BA subsequently provided estimated cabin-pressure-altitude and airplane-t1ight-altitude time history plots following decompressions-per-emergency-descent procedures, and a description ofthe BA methodology ofevaluating the threat from uncontained engine-rotor burst. 

### 1. 

### Need for exemption Section 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 

### § 25.841(a)(3) at Amendment 25-87 further requires additional considerations for a UEF that punctures and/or tears the fuselage creating a very large hole (bigger than the critical hole size). The Model CS 100 and CS300 airplanes are designed to cruise at a maximum altitude of41 ,000 feet pressure altitude. Should a UEF occur at the maximum cruising altitude, it is possible that



### 5the cabin pressure could exceed the limits contained in current regulations because the fuselagehole size the engine debris creates will exceed the allowable cabin altitudes, making it noncompliantto the above-mentioned certificationrequirements. The FAA recognizes that other airplane manufacturers have had similar difficulties meetingthis certification requirement. No airplanes that incorporate a wing-mounted engine design have been certified to fully comply with this certification requirement, and each manufacturer ofsuch designs has elected to request an exemption for airplanes where§ 25.841(a)(2) at Amendment 25-87 has been in the basis ofcertification. BA requests relieffrom § 25.841(a)(2)(ii), which specifies that cabin pressure altitude may not exceed 40,000 feet for any duration after decompression from any failure condition not shown to be extremely improbable. A grant ofexemption from this regulation would allow the Model CS I00 and CS300 airplanes' cabin pressure altitude to exceed 40,000 feet after such decompression. BA adds that the Model CSlOO and CS300 airplanes' design will meet the requirements of § 25.841(a)(2)(i) and (ii) for all system and structural failures, but not for all types ofengine failures. For some UEFs that result in pressure-vessel penetration by fragments, the design of the Model CS100 and CS300 airplanes does not meet the requirements of§ 25.841(a)(2)(i) and (ii). A grant ofexemption from this regulation would allow the Model CS 100 and CS300 airplanes to operate up to 41,000 feet, which could briefly expose cabin occupants to this altitude in the event ofa worst-case decompression (a rotor burst that would cause a 16-in. diameter hole in the fuselage). 

### 2. Conformance with applicableFAApolicy The FAA reviewed this petition in the context ofthe MSHWG Final Report on§ 25.84l(a)(2) and (a)(3), in which Bombardierparticipated, and ofour Interim Policy on Amendment 25-87 Requirements. The interim policy applies only to those decompression events which are due to uncontained engine-rotor failure. The basis ofthe interim policy is data from research on the response ofhumans and other primates to changes in ambient pressure. Evaluation ofthis data indicates a direct correlation between the alveolar partial pressure ofoxygen time integral, and the likelihood offatalities or permanentphysiological damage to those exposed to such pressure changes. That is, as the value ofthe integral increases, the likelihood offatalities or permanent physiological damage also increases. The FAA has issued a final version ofour interim policy which uses a table ofaltitudes and cumulative exposure times in lieu ofthe pressure-time integral. The values ofaltitude and time in the table, and the results ofthe pressure-time integral method, are in agreement. Accordingly, our interim policy focuses on minimizing the likelihood that. ifa person is exposed to high-altitude cabin pressure from any failure not shown to be extremely improbable, they will suffer permanent physiological damage. To analyze petitions for exemption ti·om § 25.841(a)(2), the FAA requires information about emergency descent rates, any design features that increase such rates, other design features that offset the inherent increased risk ofexposure to high-altitude cabin pressure. and operational procedures

. As stated above and in our interim policy, the FAA acknowledges a lack ofrelevant data on the effects ofexposure to high-altitude cabin pressure following decompression and,particularly,



### 6those effects on people ofvarious ages, and people with circulatory or respiratory diseases or certain other medical conditions

. Our review ofthe BApetition indicates that BA used the criteriarecommended in the FAA's interim policy. BA's design incorporates these limits to ensure airplane-descentperformance. The FAA believes that this methodology is conservative in the sense that it assumes a lower partial pressure ofoxygen than would likely be present during decompression at 41 ,000 feet. BA provides descent profiles for the Model CS 1 00 and CS300 airplanes, based on conservative estimates ofdescent performance for failure scenarios, as described in the FAA's interim policy. The descent profiles indicate that the Model CS 100 and CS300 airplanes can descend rapidly from 41 ,000 feet altitude to below 25,000 feet. BA also performed a depressurization analysis, which was based upon maximum cruise-flight conditions. 

### Itdefined the envelope ofvulnerability ofpassengers following failures that result in a decompression. In addition, BA identified design and operational features ofthe Model CS 100 and CS300 airplanes that would mitigate the effects ofan increase in cabin pressure altitude. The decompression analysis used several measures recommended in the MSHWG Final Report. However, BA did not provide an estimated severity ofexposure to high-altitude cabin pressure for occupants, based on calculation ofa Depressurization Exposure Integral (DEI) as recommended in the report. We did not consider this to be a significant deviation, as the maximum cabin altitude for which reliefis requested is 41,000 feet. The FAA reviewed BA design features and operational procedures that would mitigate the threat ofa high-altitude rapid decompression while maintainingthe descent capability ofthe Model CS 100 and CS300 airplanes, and/or ensure occupant survival. We conclude that the design features and operational procedures associated with rapid decompression, followed by an emergency descent, support grant ofan exemption. 

### 3. Review of historicaldata am/research The FAA reviewed databases from its National Aviation Safety Data Analysis Center, covering 1959 to the present. Approximately 3,000 instances, since 1959, ofloss-of-cabin-pressure have shown that system failures (e.g., cabin-pressurization controllerfailures and valve failures) and structural failures, (e.g., door-seal failures) have caused the vast majority ofthese, which typically have been recognized at low altitude within a few minutes after takeoff. Pilot error has also contributed to the numberofevents. The majority ofthese events have not subjected the occupants to exposures above 25,000 feet (an altitude considered physiologically significant). Indeed, the cabin pressure altitude in most events did not exceed 15,000 feet (the cabin pressure altitude at which passenger oxygen masks are deployed). Similarly, uncontained engine rotor-burst failures tend to be very rare. A simple calculation shows that grouping all engines and transport airplanes together yields an average probability of a UEF at cruise ofapproximately 1 x10-7 per engine hour

. New engine designs appear to reduce this probability by an order ofmagnitude. The FAA found, as noted in the MSHWG report on 

### § 25.841(a), that no fatalities from hypoxia were due to in-flight rapid-decompression events as envisioned by Amendment 25-87. The data indicate that decompression is not a significant cause offatalities. 

### Itis because these events are so rare that the FAA considers the risk to be acceptable.

7In addition, BA provided the FAA with proprietary data from its analysis ofuncontained enginerotor failures, and the size and number ofholes in the fuselage resulting from such failures. Using historical service data and theoretical values,BA performed decompression analyses for several scenarios. BA analyzed the probability ofuncontained engine-rotorfailure, and of penetration ofthe fuselage ofthe Model CS 100 and CS300 airplanes from fragments ofvarious sizes resulting from such failures. This analysis was used to assess the threat ofsuch an event to occupants ofthe airplane. The FAA did not agree with BA'sexclusion ofsome data in their analysis that concerned large holes in the fuselage causing decompression. These larger hole sizes were greater than 203 inches2 effective area and occurred from two historical events. However, BA's analysis was conducted in a manner consistent with the recommendations within the MSHWG report, and their data showed that, even for the largest survivable hole, the Model CSI00 and CS300 airplanes would be able to meet the FAA's interim-policy criteria. 

### 4. Holesfrom uncontainedengine rotor failure The FAA evaluated the BA methodology for determining hole size, in the fuselage and/or wings, caused by uncontained engine-rotor failure. We concluded that the method makes some assumptions that one could question. However, this issue is not ofgreat significance because the FAA required BAto assume a failure that produced a very large hole in the fuselage, in turn causing a sudden decompression. 5. 

### Use of supplementaloxygen As discussed below, the FAA has analyzed the BA petition in the contextofthose recommendations, the part 25 requirements pertaining to supplemental oxygen, and certain technical standards for supplemental oxygen equipment. Section 25.1441(d) requires approval ofoxygen equipment for airplanes that are approved to operate above 40,000 feet altitude. Section 25.1443 specifies the minimum mass flow ofsupplemental oxygen for flightcrew and passenger oxygen systems up to a cabin altitude of40,000 feet. Part 25 does not contain standards for oxygen systems above 40,000 feet. However, FAA Technical Standard Orders (TSOs) provide requirements for diluter-demand pressure-breathingregulators (TS0-89) and demand oxygen masks (TS0-78) up to 45,000 feet. In addition, the Society ofAutomotive Engineers (SAE) Standard AS 8027 provides specifications for diluter-demand pressurebreathingregulators up to 45,000 feet. It is the FAA's understanding that no diluter-demand pressure-breathing regulators available for commercial airplanes meet all the requirements of TS0-89 or AS 8027. As pmi ofthe certification for the Model CS100 and CS300 airplanes, BA must substantiate the adequacy ofthe supplemental oxygen systems installed for the tlightcrewexposed to cabin altitudes above 40,000 feet. Flightcrew pressure-breathing equipment requires training to ensure effective use

. Pressure breathing requires physical effort to exhale and minimal effort to inhale. This reversal ofthe normal breathing cycle can lead to hyperventilation. Training ofpassengers to use pressurebreathing equipment safely is considered impractical. The FAA determined that an acceptable means ofcompliance for the fixed and portable oxygen systems used by flight attendants and passengers would be to install oxygen equipment that is certificated to 40,000 feet, and limit exposure to the reduced pressure environment above 40,000 feet via airplane-descent performance. The FAA believes that, ultimately, occupant survival during a decompression

8event depends upon swift descent to a lower altitude. In its review ofthe petitioner's airplanedescent profile, the FAA finds that the Model CSI00 and CS300 airplanes can descend at acceptable rates. 

### 6. Conclusion ofF AA analysis Permitting airplanes to fly above 40,000 feet does offer real and tangible benefits to the aerospace industry, the traveling public, and the U.S. economy by reducing congestion, improving fuel economy, and reducing pollution

. Ifcompliance with § 25.841 at Amendment 25-87 were to limit airplane operations to a maximum altitude of40,000 feet, it 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 ofthese airplanes and the safety benefits oftheir more advanced technology. Based upon evaluation ofthe data and analysis BA provided, the FAAfinds sufficient justification for a partial grant ofexemption from § 25.841(a)(2)(i) and (ii). This partial grant ofexemption does not provide relieffrom § 25.841(a) for any other system and structural failure events not shown to be extremely improbable. The petitioner must demonstrate compliance for those failure events, and this partial grant is predicated on the beliefthat the petitioner will successfully demonstrate that compliance for the Model CS100 and CS300 airplanes. As noted in the MSHWG report on § 25.841(a), a tire burst in-flight is not extremely improbable as demonstrated by historic data. The ground loads for tires are not applicable inflight, and for this condition tires are extremely robust. According to§ 25.729(f)(l) and historic data, tire bursts do occur in-flight. It is very difficult to demonstrate that tires cannot burst in case ofoverheating. It cannot be demonstrated that tires do not burst in high-altitude flight. Therefore, the tire-burst event must be considered in the cabin-depressurization analysis. In addition, pressure-vessel openings resulting from loss ofantennas, or stall-warning vanes, or any system-failure conditions that are not shown to be extremely improbable, must be considered

. The effects ofsuch damage, while operating under maximum normal cabin-pressure differential, must be evaluated. Also, structural cracks will be addressed as perthe existing Amendment 25-87 preamble, i.e.: The maximum pressure vessel opening resulting from an initially detectable crack propagating for a period encompassing four normal inspection intervals. Mid panel cracks and cracks through skin stringer and skin frame combinations must be evaluated. In addition, this partial grant ofexemption is predicated on the requirement that the Model CSIOO and CS300 airplanes successfully demonstrate compliance to§§ 25.1441 , 25.1443, 25.1445, 25.1447, and 25.1449. This partial grant ofexemption takes into account operating rules in 14 CFRparts 91 , 121 and 135, which require that:

• one pilot wear and use their oxygen mask when operating at and above certain altitudes, and

• an adequate quantity ofoxygen is provided for crew operations.

9The FAA recognizes that BA accounts for non-standard conditions, such as rapid decompression, in defining appropriate supplemental-oxygen-system maintenance and checks at appropriate intervals that they include in the Instructions for Continued Airworthiness (ICA). To facilitate each operator's incorporation ofthis information into their maintenance procedures, BA also helps operators understand the details ofthe ICAs. BA typically accounts for non-standard conditions, such as rapid decompression and emergency descent, in developing appropriate dispatch criteriawith a malfunctioning system in the Master Minimum Equipment List (MMEL). For example, ifBA determines that dispatch is possible with a malfunctioning system that contributes to the airplane's ability to perform an emergency descent, BA could propose that the MMEL limit dispatch to a lower maximum flight altitude. Rather than identify an MMEL dispatch limitation as an explicit condition ofgrantingthe exemption, the FAA has determined that it is appropriate for the FAA Flight Operations Evaluation Board to evaluate the matter ofdispatch with a malfunctioning system. Though VMo/MMo is normally the best speed for a rapid-decompression descent, the pilots should follow the recommended emergency-descentprocedures in the Airplane Flight Manual (AFM). Rather than place an MMEL dispatch limitation as an explicit condition ofgranting the exemption, the FAA has determined that it is appropriate for the FAA Flight Operations Evaluation Board to evaluate the matter ofdispatch with a malfunctioning system that is required to ensure that the airplane is capable ofperforming an emergency descent. The applicable rapid-decompression procedures for the flightcrew must be included in the Emergency Procedures section ofthe AFM. This information must also be included in the BA Flightcrew Operating Manual. Note that initial and recurrent emergency training for all crewmembers, in accordance with§§ 121.397, 121.417, and 121.427, must include training for a rapid decompression and donning ofoxygen masks. The partial grant ofexemption from § 25.841(a)(2)(ii) will permit cabin pressure altitude to exceed 40,000 feet for one minute (but not to exceed 41 ,000 feet for any duration) after decompression from any UEF condition not shown to be extremely improbable. The partial grant ofexemption from § 25.841(a)(2)(i) will permit cabin pressure altitude to exceed 25,000 feet for more than 2 minutes (but not more than three minutes) after decompression from any UEF condition not shown to be extremely improbable, allowing time for the airplane to descend from an altitude of41,000 feet to 25,000 feet. 

### The FAA's decision In consideration ofthe foregoing, I find that a partial grant ofexemption is in the public interest regarding 

### §§ 25.841(a)(2)(i) and (ii) at Amendment 25-87. Therefore, pursuant to the authority contained in 49 U.S.C. 40113 and 44701, delegated to me by the Administrator, partial exemption from the requirements of§§ 25.841(a)(2)(i) and (ii), at Amendment 25-87, is granted for The Bombardier Aerospace Company CSeries Model BD-500-1A10 (CS 1 00) and BD-500- 1

A

### 1I (CS300) airplanes. This partial grant ofexemption is subject to the following conditions: 

### 1. The AFM for the Model CS

### I00 and CS300 airplanes must indicate that the maximum indicated operating pressure altitude is 41,000 feet.

102. The AFM must contain applicable tlightdeck crew procedures for a rapid-decompression event. The section ofthe AFM, for the Model CSI00 and CS300 airplanes, that pertains to actions in the event ofa decompression, must state that the tlightdeck crew should initiate a descent at the maximum rate ofdescent and safe descent speed, which typically is the maximum operating speed (VM o/MMo), assuming structural integrity ofthe airplane. 3. The petitioner must submit certification flight-test data for the CSeries Model CSl00 and CS300 airplanes simulating the loss ofone engine (i.e., from an uncontained engine-rotor burst), and subsequent loss ofsystems associated with the loss ofone engine, that corroborate the descent profiles used in the analysis to show that, after decompression at an airplane indicated operating pressure altitude of41 ,000 feet, the cabin pressure altitude will not exceed 25,000 feet for more than 3 minutes or40,000 feet for more than I minute.

Issued in Renton, Washington, on 

## FEB 02 2015



# ?#!;['

_ fL___

.

Jeffrey E

. Duven Manager, Transport Airplane Directorate Aircraft Certification Service

II