1 Transport Airplane Directorate 1601 Lind Avenue, S.W. Renton, W ashington 98057 - 3356 April 30 , 2013 Mr. Keith Barnett Airworthiness Manager, CSeries Bombardier Aerospace 400 CÔTE

- VERTU Rd. West Dorval, QUÉ BEC, Canada H4S 1Y9 Dear Mr. Barnett ; The Federal Aviation Administration ( FAA ) has completed our review of your pe tition 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 M odel s BD - 500 - 1A10 (CS100) and BD - 500 - 1A11 (CS300) airplanes , dated No ve mber 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 t he 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 Bo mbardier 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). Bo mbardier provided no results of their decompression anal ys is (e.g., airplane cabin pressure time history) or comparisons with d ata from uncontained e ngine d ebris trajectory studies. Bo mbardier did not provide an estimate of the critical hole size which would result in a decompression which the airplane would successfull y meet the cabin pressure limits contained in 14 CFR 25.841(a)(2). Bo mbardier2

did not provide any

estimates of the resulting fuselage hole size versus probabi lity of occurrence. (2) On several pages Bombardier refers to the Aviation Rulemaking Advisory Committee (ARAC) Mechanical S ys tems Harmonization Working Group ( MSHWG ) report , but nowhere in the petition does Bombardier provide an assessment of the severi ty 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 Memo randum 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. Bo mbardier did not provide any estimates of the severity to the occupants (e.g., the Depressurization Exposure Integral (DEI) method in the ARAC MSHWG Report). Bo mbardier 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 desig n 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:** T he 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. ” Bo mbardier has not provided m any details o n mitigating design and/or operational features that offset the increased level of risk at high altitudes (e.g., Does the CSeries incorporate any redundant s ys tems that provide additional descent speed capability , or include additional containment protection from engine debris , etc. ? ) and, Bo mbardier 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 anal ys is (e.g., hole size, environmental control s ys tem pack operation, availab le h ydraulic/electrical/pneumatic power to operate control surfaces, discharge coefficient of hole, other airplane leakage, etc.). Inaddition, Bo mbardier did not provide any estimated airplane descent rates which cover the operating envelope (e.g., bounda ries set b y maximum and minimum airplane weight) . Also , Bombardier did not provide any airplane3

performance predictions to show that the CSeries can successfull y meet the cabin pressure exposure limits in the Policy Memo ANM - 03 - 112 - 16. (4) Bombardier i s asked to confirm their intention to conduct flight test certification demonstration of the proposed flight test emergency descent procedure s (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 sy stem . Please provide an explanation of associated hardware and software architecture, sy stem 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 M odel s 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 L ind 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 an y questions or concerns regarding this request, please contact Stephen Happenny, ANM - 112 , at 425 - 227 - 2147 , or e - mail, Stephen.Happenn y @faa.gov. Sincerel y,

Victor W icklund Manager, Propulsion & Mechanical Sy stems Branch Transport Airplane Directorate , Aircraft Certification Service