# ~AIRBUS

FAA Seattle 1601 Lind Avenue Renton Washington 98055-4056 USA Attn: Mr

. Tim Dulin Stefan Lobel T +494074373133 F E stefan

. loebel@airbus

.com Our Reference : D21 M 15000084 Your Reference : 06 January 2015

Airbus Petition for Exemption from 14 CFR 25.841(a)(2) and (3) for A320NEO family

Dear Sir,
Attached please find the airbus Petition for Exemption from 14 CFR 25.841 (a)(2) and (3) for Airbus A320NEO family for your review.

Your concurrence is kindly requested

Best regards Digitally signed by Stefan loebel

- SIG ON: c:DE, a: European Aeronautic Defence and Space Company, ou=Employees and Contractors, ou=DA GmbH, cn:=Stefan Loebel SIG, seriaiNumber::: 138805 Reason : I am the author of this document. location: Hamburg Date: 2015.01.07 10:00:09 +01'00' Stefan Lobel (CM)

Copy : EASA PCM G

. Scannapieco 

### ei)AIRBUS Digitally s1gned by Cecile WilherSIG ON: c=DE, o:European Aeronautic Defence and Space Company, ou=Employees and Contractors, ou=Airbus SAS, cn=Cecile WilherSIG, seria\Number=236600 Reason: I am the checker of th1s document. location: Toulouse Date: 2015.01.07 10:20:02 +01'00' Cecile Willier (MCC)

Cl Altus Operabons GmbH, 2015

. AI nghts reserved Confiden!Jal and IJ"oprietary document. This document and allmformaboo contamed here1n 1s the sole IJ"Operly of A.nbUs Operations GmbH No mtellectuai!J"operfy nghts are granted by the delivery of th1s doct.ment or the discloslJ'e of its content Th1s docunent shall not be reproduced or disclosed to a tlurd party Without the express wntten consent of Airbus Operations GmbH Th1s document arld 1ts content shall not be used for any purpose otha than that for whiCh rt ts supplied Airbus Operation s GmbH P

.O. Box9501 09 , 21111 Hamburg , Germany Offices: Kreetslag 10, 21129 Hambu rg, Germany Phone +49 (0) 40 743-70 Fax +49 (0) 40 743 44 22 Legal domicile : Hamburg Business Address: Kreetslag 10 , 21129 Hamburg , Germany Registration court and number: Amtsgericht Hamburg HRB 43527 Chairman of Supervisory Board : Fabrice Bregier Board of Management: GUnter Butschek, Chai rman & CEO Mario Heinen , Or. Thomas Ehm , Oliver Vogelgesang

### Petition for Exemption from 14 CFR 25.84l(a)(2) and (3)

Petitioner:

Contact in France: Airbus SAS I Rond Point Maurice Bellonte 31707 Blagnac Cedex France

Yves Regis Vice President, Product Integrity (EIA) Starpark 022-265 BP 0 2202 33.(0)5.61.93.30.28 Yves.Regis@airbus.corn

Reference: SA2 1 D 13020794

### TABLE OF CONTENTS ACRONYMS 1. SUMMARY OF INFORMATION REQUIRED BY 14 CFR 11.81 4 1.1 SPECIFIC SECTIONS OF THE FAR FROM WHICH WE SEEK EXEMPTION 4 1.2 EXTENT OF RELIEF SOUGHT, AND REASONS 4 

### 2. REASONS WHY GRANTING THIS REQUEST WOULD BE IN THE PUBLIC INTEREST 5 3. REASONS WHY GRANTING AN EXEMPTION WOULD NOT ADVERSELY AFFECT SAFETY 5 4. SUMMARY FOR FEDERAL REGISTER 6 5. REASONS FOR REQUESTING EXERCISE OF THE PRIVILEGES OF THE EXEMPTION OUTSIDE THE UNITED STATES 6 6. SUPPORTING INFORMATION 6 6.1 TEXT OF FAR 25.841 (A), AT AMENDMENT 87 6 6.2 GENERAL DISCUSSION -GROUNDS SUPPORTING EXEMPTION 7 

### 7. UNCONTAINED ENGINE ROTOR FAILURES (UERF) 9 7.1 GENERAL 9 7.2 IMPLEMENTED MEANS TO REDUCE UERF ON A320 NEO 9 

### 8. A320 NEO DESCENT PERFORMANCE 10 9. INFLUENCE OF HOLE SIZE ON CABIN PRESSURE TIME HISTORY 11 10. RESULTS OF THE ARAC MSHWG WORKING GROUP 11 11. DEl METHOD APPLIED TO A320 NEO AND COMPARISON WITH FAA INTERIM POLICY ON HIGH ALTITUDE CABIN DECOMPRESSION 14 12. PUBLIC INTEREST 16 REFERENCE DOCUMENTS 17

### ACRONYMS AC A/C AECMA AFA AlA AMM ALPA ARP ATA ARAC CAM I CFR CPCS DEl DSI FAA FADEC FAR FL GAMA HBR ICAO JAA JAR LBR MSHWG RVSM SAE UERF Advisory Circular Aircraft European Association of Aerospace Industries Association of Flight Attendants Aerospace Industry Association Aircraft Maintenance Manual Air Line Pilots Association Airspace Recommended Practice Air Transport Association Aviation Rulemaking Advisory Committee FAA Civil Aerospace Medical Institute Code of Federal Regulations Cabin Pressure Control System Depressurisation Exposure Integral Depressurisation Severity Index Federal Aviation Administration Full Authority Digital Engine Control Federal Aviation Regulation Flight Level General Aviation Manufacturing Association High Bypass Ratio (Engines) International Civil Aviation Organisation Joint Aviation Authorities Joint Aviation Requirements Low Bypass Ratio (Engines) Mechanical Systems Harmonization Working Group Reduced Vertical Separation Minimum Society of Automotive Engineers Uncontained Engine Rotor Failure

### 1. SUMMARY OF INFORMATION REQUIRED BY 14 CFR 11.81
1.1 SPECIFIC SECTIONS OF THE FAR FROM WHICH WE SEEK EXEMPTION Exemption from strict compliance with parts ofthe requirements of 14 CFR 25.841 (a)(2)(i) and (ii) and (3) is sought for the AIRBUS models A319-171 n, A319 -1 51 n, A320-271 n, A320-251 n, A321- 27 1 nand A32 1-251 n, further referred to as the A320 NEO fami ly of aircraft. 

### 1.2 EXTENT OF RELIEF SOUGHT, AND REASONS Relief is sought from the requirements applied by FAA that compliance with 14 CF R 25.841 (a)(2)(i) and (ii) be shown for some uncontained engine rotor fai lure (UERF) scenarios. With this petition, it is Airbus understanding that system and structure failures according to 1 4CFR25.841 (a)(3) are excluded for the demonstration in regard to 14 CFR25.841 (a)(2)(i) and (ii) since the functions involved in the pressurization and pressure contro l of the fuse lage remain unchanged relative to the A319- l II , A319-131, A320

-2 11 , A320-231, A32 1-ll I, A321 -1 31, A32 1-2 1I and A321-231 including all weight variants , further referred to as the legacy A320 aircraft type. To analyse petitions for exemption from 

### § 25.84 1 (a)(2) applicable to reference Amendment 25 -8 7 and later amendments, the FAA has published an Interim Policy on High Altitude Cabin Decompression [ 19] to address only to those decompression events which are due to UERF. This policy focuses on minimizing the likelihood that, if a person is exposed to high-altitude cabin pressure from any fai lure not shown to be extremely improbab le, he will suffer permanent physiological damage. 

### It is mainly based on data from research on the response of humans and other primates to changes in ambient pressure. Evaluation ofthis data indicates a direct correlation between the alveolar partial pressure of oxygen time integra l and the likelihood of fatalities or permanent physiological damage to those exposed to such pressure changes. As a resu lt, as the value of the integral increases, the likelihood offatalities or permanent physiological damage also increases. To simplify the FAA accepted " pass/fai l criteria," the FAA has issued a final version of the Interim Policy aim ing to consider the result of investigations for a revised cabin pressurization standard which was the subject of an Aviation Rulemaking Advisory Committee (ARAC) task
. 

### It uses a relationship of altitudes and cumulative exposure times in lieu of the pressure-time integral. According to this , the primary means to ensure occupant survivability rests in quick l y bringing the occupants to a cabin pressure where they can survive (i.e. , a lower cabin pressure altitude). To be eligible for an exemption , the applicant' s design should therefore show compliance with the time limits given by the aforementioned relationship
. With this petition it is shown that the Airbus A320 NEO family of aircrafts uses design features that facilitate rapid airplane descent from high altitudes to ensure that the occupants will not be subjected to pressure altitudes for durations longer than those given by the altitude-exposure-time relationship of the interim policy [ 19]. Granting this exemption does not set a precedent as the facts and circumstances of this situation are similar to those that led FAA to grant Exemption No
. I0228 for the Airbus A350XWB.

### 2. REASONS WHY GRANTING THIS REQUEST WOULD BE IN THE PUBLIC INTEREST

• The A320 NEO aircraft variant is unmodified with respect to the requirements of 14CFR25
.841 (a)(2)(i) and (ii) and (3) for the consideration of system failure events. An exemption is requested for cabin decompressions that can occur from uncontained engine rotor failures that result in large holes in the fuselage. Airbus believes , based on fleet service experience , that these are rare events. The new engine option (NEO) introduced on the A320 family of aircraft and associated modifications necessary for the integration comply with the latest FAA requirements and, therefore, offer a significantly higher basic level of safety relative to previously certified transpmt category aircraft
.
• Approval for operation up to 41 ,OOOft will enable the air traffic system to provide more capacity , and hence more aircraft separation and safety , without adversely affecting the safety of the passengers .
• Approval for flight at 41 ,OOOft will enable the A320 NEO family of aircraft to compete fairly with other existing aircraft that are not subject to the same requirements, without causing any adverse effects to the passengers .
• Approval for operation up to 41,000 ft will also serve the public interest via the use of the newest generation ofengines available today , and permit them to operate where they offer lower emissions, and higher fuel efficiency.

• Approval for flight at 41 ,OOOft provides for more economical operation ofthe A320 NEO family of aircrafts reducing the cost to the travelling public
. 

### 3. REASONS WHY GRANTING AN EXEMPTION WOULD NOT ADVERSELY AFFECT SAFETY The A320 NEO family of aircraft making re-use of the cabin pressure control system fi·om the Airbus conventional engine option (i.e. the legacy A320 family of aircraft, further referred to as "CEO") complies with FAA requirements issued at the date of the A320 CEO regarding cabin decompression but due to engine modification of the NEO variant, the compliance with the latest amendment of 14CFR 25 has to be re-assessed for some extremely rare UERF event scenarios
. Calculations can be used to show an increase in theoretical "risk" to passengers if these extremely rare scenarios are followed
. However, an examination of the basi s for these risk assessments as described in the available phy siological data shows that this very small theoretical increase in risk is far smaller than , and certainly within the variability of results from examination of available physiological data ([3] to [ 15]). There is , therefore , no basis for assessing a real increase in risk from the conditions that prevail with a grant ofthis exemption. For such rare UERF scenarios , the FAA has published a policy [19] , titled ,Interim Policy on High Altitude Cabin Decompres sion (Reference Amendment 25-87)' , which provides from a safety point of view acceptable exposure time limits for high-altitude cabin decompre ssions from any failure not shown to be extremely improbable before permanent physiological damage would occur. By showing information about emergency-descent rates as requested by the policy , including any design features that increase such rates , other design features that offset the inherent increased risk of exposure to high-altitude cabin pressure, and operational procedures, Airbus concludes the theoretical risk from such decompressions to passengers be acceptably minimised
.

### 4. SUMMARY FOR FEDERAL REGISTER The A320 NEO family of aircraft re-uses the cabin pressure controls system including the pressurization system and therefore it is claimed that compliance with the requirements of 14CFR25
.841 (a)(2)(i) and (ii) and (3) for system fa ilure events does not need to be shown. An exemption is requested to 14CFR 25.841 (a)(2)(i) and (ii) and (3) for those cabin decompression s which can occur from uncontained engine rotor fai lures (UERF) that result in holes in the fuselage exceeding a geometric area of A 1 (A 1 : defined in Appendix I ofthis petition for exemption) 

### 5. REASONS FOR REQUESTING EXERCISE OF THE PRIVILEGES OF THE EXEMPTION OUTSIDE THE UNITED STATES The exemption sought pe1iai ns to design requirements of 14 CFR 25. If granted, the exemption wi ll resu l t in an FAA certificated aircraft design that embodies the privileges of the exemption, and the operation of these aircraft will include flights outs ide the United States. Exercise of the privileges of the exemption outside the United States is therefore required. The exemption requested does not in

vo lve a specific ICAO standard, and a filing of a difference with I CAO would not be required
. 

### 6. SUPPORTING INFORMATION 6.1 TEXT OF FAR 25.841 (A) , AT AMENDMENT 87 The fo llowi ng request for exemption for the Airbus A320 NEO fami ly of aircraft is limited to the requirements as set forth in FAR 25.841 (a)(2)(i) and (ii) and (3), Amendment 25

-87
. Specifically, while the A320 aircraft is unmodified with respect to the requirements of 14CFR25.841 (a)(2)(i) and (ii) and (3) for all system and structural failure events , due to the incorpora

tion of new engines with higher bypass ratios and larger fan diameters there are some decompressions caused by UERF events for which A3 20 NEO cabin pressure altitudes and /or time would exceed those limits. An exemption is requested from 14 CFR 25.841 (a)(2)(i) and (ii) and (3) for tho se cabin decompressions which can occur from UERF events that result in holes in the fuselage exceeding the geometric area A 1 (see Figure 2- 1 and Figure 2-2 ofAppendix 

### 1). The cun·ent regul atory requirements as contained in FAR 25.841 Pressurized Cabin at Amendment 25- 87 states , 

### (a) Pressuri zed cab ins and compartments to be occupied must be equipped toprovide a cabin pressure altitude of not more than 8, OOOfeet at the maximum operating altitude of the airplane und er nor mal o perating conditions. (/)Ifcertificationfor operation over 25, 000 feet is 

### requested, the airplane must be des i gned so that occupant s will not be exposed to cab in pressure altitudes in excess of 15,000feet after any probable failure condition in the pressurization system. (2) The airplane must be designed so that occupants will not be exposed to 

### a cab in pressure altitud e that exceeds thefollowing after decompress ionfrom any fa ilure condition not shown to be extremely improbable: (i) 

### Twenty-jive thousand (25 ,000)feetfor more than 2 

### minutes; or (ii

) F arty thousand (40, 000)feetfor an y duration. (3) Fuselage structure. engine andsystemfa ilures are to be cons id ered in evaluating the cab in decompression.

### 6.2 GENERAL DISCUSSION - GROUNDS SUPPORTING EXEMPTION Airbus respectfully submits that compliance with subsection (2)(i) and (ii) and (3) of the above referenced regulation will likely have an adverse market impact on the Airbus A320 NEO family when operated in the USA airspace
. Airbus fut1her submits that the difficulties , which the Airbus A320 NEO family of aircrafts will experience in meeting these requirements , are similarly shared by other manufacturers of regional and large transport category aircraft with wing mounted engines for which new or amended Type Certificates will be sought. For aircraft designs incorporating wing mounted engines FAA provides guidance that the "engine failures" that should be considered in evaluating the cabin decompression include a 1/3 fan disc tangentially penetrating the pressurized fuselage (consistent with JARJCS/FAR 25.903(d))
. For aircraft designs incorporating wing mounted engines this tangential fuselage strike scenario results , especially for cabin volumes of short to medium range aircraft including the Airbus A320 family , in a cabin depressurisation fast enough to reach in less than I0 seconds outside ambient pressure in the cabin. With currently available technology it is impossible to descend a passenger aircraft of A320 NEO size at high take-off weight from maximum cruise flight level down to 40 ,000 ft within I0 seconds , as required indirectly by FAR 25
.841 (a)(2)(ii). In addition , when considering pilot reaction time and the weight of the A320 NEO family of aircrafts it is impossible to reach FL250 within 2 minutes (FAR 25
.841 (a)(2)(i)) after a rapid decompression occurs at maximum cruise flight level (FL398 respectively FL41 0). As a practical matter, compliance to FAR 25.841 (a)(2) and (3) can only be achieved for such aircraft by restricting flight ceilings. A limitation of the maximum operating altitude would prevent the A320 NEO family of aircrafts from operating competitively and economically as compared to existing aircraft fleets in the U.S. airspace. In order to comply with the 25.841 (a)(2) regulation as written , the A320 NEO family of aircrafts would have to limit their maximum operating altitude to a level that would be far below FL400
. The existing airplanes can cruise at higher altitudes where they are more fuel-efficient. Under typical operational conditions, a limitation of maximum flight level would cause either a significant range deficit or a major block fuel increase
.. It should also be noted that current EASA regulations will enable the Airbus A320 NEO family of aircrafts to fly up to a ceiling of 41 ,000 feet without any operational restrictions for European operators , whereas American operators would be operationally penalized with an U.S. registered A320 NEO due to higher fuel bum and reduced range. Furthermore, limiting the maximum cruise flight level of new generation airplanes to lower altitudes will result in higher traffic density , which could lead to greater collision risk if not otherwi se mitigated
. In anticipation ofthis increased level of risk, additional costs may be imposed on the aviation system , in order to maintain an acceptable level of safety
. Larger separation minima may be required , resulting in more delay , and less growth potential for U.S. economy. Airbus respectfully submits that continuing to allow operation in the less congested airspace above 40 ,000 feet will enhance safety
. Previously certified large transp011 aircraft incorporating established design practices have operated at altitudes in excess of 40 ,000 feet for more than 20 years. Historically , relatively few accidents or incidents have occurred due to rotor burst during cruise. It is important to note that decompression incidents that have exposed an aircraft cabin to pressure altitude profiles with risk of injury to passengers are very rare events . Decompression events resulting from engine rotor burst are even more remote [ 16] , [20].

### Industry history reveals that few cases of catastrophic decompressions at high altitude have occurred, and those that have occurred involve in their majority small business jets. This is supported by the AlA Committee Report on High Bypass Ratio Turbine Engine Uncontained Rotor Events [20] which , by a data reduction on engine rotor burst events covering the period from 1969 to 2006 , concludes a rate of 3
.5E-8 per engine cycle for basic rotor burst events , averaging 2nd and 3rd generation turbofan engines. For 3rd generation turbofan engines, the basic rotor burst rate is quoted to be less than 2.5E-8 per engine cycle. This is substantiated by a 5 years rolling average that reveals a rate of 2.1 E-8 per engine cycle. The FAA assigned the Aviation Rulemaking Advisory Committee (ARAC) and the Mechanical Systems Harmonization Working Group (MSHWG) the task of addressing various concerns raised by the 25
.841 (a) regulation and of reaching a consensus among expe1is from the FM, JAA , ATA , ALPA , AFA and Aircraft Manufacturer members with representation in the AlA, AECMA or GAMA
. The MSHWG issued their final rep01i in July 31st, 2003 and recommended the use of the decompression exposure integral (DEI) method to assess the physiological effects of a decompression event on aircraft occupants [I] , [3] , [II] , [ 13] , [ 15]. Airbus has used the recommendation ofthe MSH WG to show that, assuming a worst case depressurisation event, physiological effects to the aircraft occupants stay well within the recommended limits ofthe MSHWG (see Section 10 ofthis petition)
. In 2006 the FAA issued memorandum ANM-03-112-16 [19] that provides an Interim Policy on decompression issues associated with high altitude flight for the period oftime until a new rule is available
. This memorandum details how the FAA will evaluate petitions for exemption from FAR 25.841 , at amendment 25-87
. The requirements of[l9] are as follows: Cabin Pressure Altitude Maximum Total Exposure Time lminutesJ 

### Above 45000 0 Above 40000 I 

### Above 25000 3 Above 10000 6 Airbus will show in Section 8 and Appendix I, Section 3 ofthis petition that the A320 NEO family of aircraft embodies design features that enable compliance with this requirement. It is wo1ih noting that cuJTent aircraft standards contain already design features in order to minimize cabin decompression hazards for occupants:
• It 

### is today a worldwide standard on all civil transport aircraft to have First Aid Oxygen onboard for occupant hypoxia treatment. As per JARJCS/FAR 25.1443(d) and JAR/CS/FAR 121.333(e)(3) First Aid Oxygen needs to be canied in the cabin for at least two percent of the occupants able to provide an average flow of 3 litres of oxygen per minute for the entire flight after cabin depressurisation occmTed
. The purpose of First Aid Oxygen is to treat those occupants that have suffered from hypoxia by providing the maximum possible blood oxygen saturation level in order to ensure best possible recovery [7].

• FAR 25
. 1447(c)(3)(ii) requires the flight crew be given pressure demand type oxygen dispensing equipment if decompressions that are not extremely improbable may expose the flight crew to cabin pressure altitudes in excess of 34 ,000 feet. Compliance with the rule ensures the flight crew will retain the ability to safely operate the airplane following a decompression 

### [I I].• As per JARJCS/FAR 25.1443(c) passengers and flight attendants need to be suppl ied with supplemental oxygen. Those means have been developed and introduced to sufficiently protect cabin occupants against physiological harm of hypoxia. It has been shown by various tests that the supplemental oxygen system provides an adequate protection against hypoxia if masks are correctly used as shown during the safety briefing before each flight [3] , [6]
.
• Section 25.144 1 (d) requires that the oxygen flow rate and the oxygen equipment used in airplanes operating at high altitudes must be approved
. The combination of emergency descent rate documented in this petition, along with the FAA approved oxygen masks and associated oxygen flow rates with which the A320 NEO family of aircrafts are equipped, are adequate to protect the passengers from adverse consequences of a worst case cabin decompression.


### 7. UNCONTAINED ENGINE ROTOR FAILURES (UERF) 7.1 GENERAL CuJTent design practices for large commercial transports have evolved such that placement of the engines is accomplished via attachment to pylons located underneath the wings. While permitting benefits to stabi lity and airplane performance, this feature exposes a large area to potential penetration ofthe pressurized vessel in the event of an UERF. Smaller commercial airplanes have typically attached the engines to the fuselage. The aft pressurized bulkhead has been placed immediately forward of the rotor burst zone. Traditionally this has limited pressurized fuselage penetrations to no more than a few small fragments. This concept might be safer in terms of cabin depressurisation but it provides a higher risk of engine debris hitting the second engine due to its proximity.


### 7.2 IMPLEMENTED MEANS TO REDUCE UERF ON A320 NEO The A320 NEO will have third generation high bypass ratio engines that wi ll have the following de

sign features 

### I maintenance procedures 

### in order to minimize the occmTence of uncontained engine failures:

• The engines will be equipped with a fan containment ring that reduces the "un-containment" risk at fan level. The fan is considered to have the highest damage potential compared to turbine and compressor stages.

• Several FADEC protections like over speed protections and vibration indications will be implemented in order to reduce the risk of abnormal engine behaviour (including UERF).

• Engines are regularly inspected externally and internally to detect blade damages. After foreign object ingestion by the engine such as debris , bird and ice the AMM procedure requires checks in order to evaluate the damage.

• Engine manufacturers have made progress in developing material more robust to thermal and mechanical stress. The A320 NEO engines will profit from those material improvements , which will further contribute to a reduced probability ofrotor burst events.

### 8. A320 NEO DESCENT PERFORMANCE The A320 NEO descent capabilities for the PW II 00 G-JM as being identified " worst case' ' in terms oftime to descent to FL250 and FL I00 is shown in Appendix I, Figure 2-3. This envelops the descent performance ofA319 and A321 NEO variants for both , ceiling altitudes of41 ,OOOft and 39 ,800ft. The following assumptions have been made:

• For the A320NEO family of aircraft, like on all other Airbus programs, the flight manual will recommend to use the autopilot for the emergency descent. This will relieve workload from the flight crew and provides a smooth start for the emergency descent in order to avoid head injuries in the cabin. The provided curves in Figure 2-3 represent autopilot descents
.
• In the event of an uncontained engine failure , it is assumed that other, unrelated system or structural failures do not occur at the same time. This means for the scenario of a worst case damage ofthe pressurized fuselage it can be assumed that all hydraulic systems are available (except the hydraulic pumps linked to the failed engine) and no spoiler has been damaged (recommendation from the ARAC working group , and detailed in Interim Policy on High Altitude Cabin Decompression [ 19])

• The airplane is designed such that in the event of an UERF the airplane structure, systems and other engines functions enable a Ymo/Mmo rate of descent. For the autopilot descent the speed is slightly below that value : Ymo/Mmo- 5 kts
.
• The curves of Figure 2-3 are based on data that have been established by simulation (IFP software using engine/loop2 and QDV/loop3 databases) verified by flight test for the CEO sharklet configuration. Past experience has shown that in pmticular in terms of spoiler deflection angle margins are required in order to address uncertainties in terms of buffeting and handling qualities. Therefore, a margin of 10% has been added to the calculated values, which means that the descent time of Figure 2-3 represents II 0% of the calculated time
. It should be noted that:

• The maximum spoiler deflection angle depends on aircraft weight (the heavier the aircraft the lower is the spoiler deflection angle)
. The maximum spoiler deflection angle is automatically determined by the flight control system and does not require specific pilot actions (common descend procedure for all A320 NEO weight configurations)
.
• The maximum aircraft weight at maximum operating altitude (41 ,OOOft) is 

### Wl 

### ** *. This value depends on the engine thrust and buffet onset and is therefore subject to changes during the aircraft development process.

• The longest descent time that is required to descend from the same altitude of occurrence down to IO ,OOOft is for an A320 NEO that weighs 

### W 2 ***, which is for the A319 NEO nearly the same weighing 

### WJ * ** or 

### W2 ***
.
• Both profiles 

### (Wl and 

### W2) provide the envelope for the A319/320/32 1 NEO emergency descent time
. All other configurations in ten11S ofweight and altitude require less descent time.

• The provided descent profiles are based on ISA temperature conditions.

* **)WI and W2 are defined in Appendix I, Section 1-2 and Figure 2-3.

### 9. INFLUENCE OF HOLE SIZE ON CABIN PRESSURE TIME HISTORY The hole size and its effects on the cabin pressure time history have been investigated and are shown in Figure 2-2 ofAppendix I. For holes smaller than A 1 the cabin pressure altitude does not exceed 2 minutes above 25,000ft, whereas it requires a hole ofA2 ** to exceed 40,000ft cabin altitude. The provided data are based on the 

### "Wl descent profile" of the A320 NEO variant powered by PW II OOG-JM , which represents the worst case for time spent above 25,000/40 ,000ft cabin altitude. The structurally survivable hole size which has already catastrophic consequences on the airframe structure has been used for all further calculations ofthe cabin pressure time history (Appendix I, Section 2, Figure 2-4 and Figure 2-6). 

### It refers to a tangential cut length of 1313mm from 1/3 disc penetrating the pressurized fuselage (consistent with JARICS/FAR 25.903(d)) which yields the total area of each critical hole size with the fan fragment thickness of 391 mm for CFM Leap 1-A and 325.4mm for the PW II OOG engine, i.e. A 3

_cFM 

### = 0 .257m2 ** and A3

_ rw 

### = 0.213m 2 **, respectively
. Even though the rragment size appears to be larger for the CFM Leap 1-A engine, the calculations shown in Appendix I are based on PW I IOOG-JM engine selection since the aircraft emergency descent performance significantly dominates the results the cabin pressure time history. **)As per AC 25-20 a discharge coefficient of0.5 has been assumed 

### 10. RESULTS OF THE ARAC MSHWG WORKING GROUP The MSHWG report recommended the use of a means of compliance to the requirements of FAR 14CFR25.841 (a) via an approach designated as the Depressuri sation Exposure Integral method (DEI). The method defines the envelope of vulnerability of passengers for permanent phy siological harm during a cabin depressurisation. The method assumes conservatively that passengers are not provided with supplemental oxygen. The MSHWG discovered that when the decompression data rrom decompression studies (References [4] , [5] and Figure 10-1) were evaluated with the use of an alveolar partial pressure of oxygen (i.e. , a lung pressure) time integral, a trend became clear. There is a direct correlation of the integral in that as the value of the integral increases , there is an increasing likelihood of permanent physiological damage. For the DEI method the first step was obtaining a relationship called the Depressurisation Severity Index (DSI)
. This relationship provides a measure ofthe severity of the depressurisation to atmospheric total pressure and was determined from published data (Reference [7]) and by calculation (see Figure I0-2). The MSHWG proposed the lung partial pressure of oxygen time integral method to assess physiological risk to the occupants and called this measure the 

### De pressurisation Exposure Integral (DEI). The integral is based on the period oftime in seconds that the lung partial pressure of oxygen is below 30 mmHg or 60 mmHg [see Figure 10-3]. Note that historically FAA has referenced I0,000 feet [approximately equivalent to DSI of 60 mmHg] and 25 ,000 feet [approximately equivalent to DSI of 30 mmHg] as critical points in the cabin pressure altitude , and these were selected as reference conditions. DEI below 30 mmHg and 60 mmHg provides a measure ofthe severity ofthe depressurisation event. Figure 2-4 and 2-6 of Appendix I presents the cabin altitude- time history of a depressurization event resulting rrom a A 3 hole and depicts the resulting values for DEI 30 and DEI 60 in Figure 2-5 and 2-7. Both values are well below the threshold recommendation defined by the MSHWG.g**~**

# ~ "' 0 

# 5
:::> ::!!: <A 60000 ' 1
soooo .L**~'01)**

30000

20000



# - HYPOBARIC CHAMBER EXPERlM£NTS Time Variation of Simulated Cabin Altltude

ntlE{m ln) 

### Fl GURE I0-1: Pressure time history for the altitude chamber experiments conducted in [ 4]& [5]

120

0 0 DETERMINATION OF DEPRESSURIZATION SEVERITY INDEX (DSf) AS A FUNCTION OF AIRCRAFT CABIN PRESSURE 

# I For Cabin Pressure atu;we 411.11:9 mmHg 

# I OSI "'0
. 1752 • (Cabon Pressure}- 30
. 176 

# I For Cabin Pressure between 291,9-95 mmHg and AH.89 mmH'g 

# / I __... OSI =< 0.0004441 • {Cabin Pressure )2

- 0.2209 • (Cabin Pressure)+ 57.625
For Cabin Press.ure between 47.(1 mmHg and 291.905 mmlfg 

# I
OS ! : 1G.004 •**Ln(C<~bin** Pressure l- 6S.312

# /~ 

# v 

# .., """""""**~** 

# /**~**
100 200 100 400 500 700 CABIN PRESSURE (tl'ilnHg) 

### FIGURE 10-2 : DSI versus cabin pressure 

# ....

11001:W 

# I 1 10 100

## ~ 90 

### s eo**~** -.:: 10 

# .. t 6() en c

. 0 M**~** :J 40 

## ... ::l 

## "'**~** 

## "' Ol Q. 20 

# .. Cl 10 0 0 2 3 7 TIME(min) FIGURE 10-3: Integral

- DEI30/DEI60 Note : The Figure I0-4 graphically depicts the DEI30/DEI60 for an event where the cabin pressure reaches 51 ,000 feet pressure altitude . The integral is calculated based upon the difference in DSI and the given reference condition (i.e. , 30 mmHg)
.
As noted in the MSHWG report, it was observed that a direct correlation ofthe DEI to increasing likelihood of permanent physiological harm exists. The MSHWG found that a value of 2,700 mmHgsec for the DEI30 represents the threshold at which permanent physiological harm started on tested animals (Maximum Never to Exceed Value). The same was observed for DEI60 at 15 ,000 mmHg-sec [see Figures 10-4 and 10-5 below].

;;; 6, .! .E**~** :::s 

# .. 0 c.. )( w c 0**~** .!:! 

### :; 

# .. .. Q) 

# a Q) c HYPOBARIC CHAMBER EXPERIMENTS Comparison of DEI60 walues**25 ooo** **---···-··-----------------··--------·--------·····----------·-·······-·-·······--·-·--···- ;;;=:;=;===;:;~:;:;===;;=;** **··· l**  

### I El Time duration uncler 60 mmHg (in sec x 10) 22241
20000

15000

10000

5000

0 Nicholson - Nicholson - Brierley- Brierley- Nicholson - Brierley- Hans Ernsting ''8 in " Ernsting ''6 in" Nicholson ''8 in" Nicholson '7 in" Ernsting "4 in " Nicholson ''6 in " Cia mann

1 baboon 4 baboons 7 macaques 7 llU3ClH1UeS 4 baboons 7 macaques 1 human Survival: 0 in 1 Survival: 3 in 4 Survival: 7 in 7 Survival : 7 in 7 Survival: 4 in 4 Survival: 7 in 7 Survival : 1 in 1 Recovery: 0 in 1 Recovery: 1 in 4 Recovery: 7 in 7 Recovery: 7 in 7 Recovery: 4 in 4 Recovery: 7 in 7 Recovery: 1 in 1 Figure I0-4 : DEI60 valuesHYPOBARIC CHAMBER EXPERIMENTS Comparison of DEIJO walues 6000 ,.................................................................... 5338 5000

4000

3000

2000

1000

0 Ni cholson- Nicho lso n- Brierley- Brierley . Nicholson - Brie rl ey. Hans Ernstin g "'8 in" Ernsting ''6 in" Nicholson ''8 in" Nicholson '7 in" Ernsting "4 in" Nicholson "6 in" Clamann

1 baboon 4 baboons 7 macaques 7 macaques 4 baboons 7 ma ca ques 1 human Survival: 0 in 1 Survival: 3 in 4 Surviva l : 7 in 1 Survival: 7 in 7 Survival: 4 in 4 Su rvival: 7 in 7 Survival : 1 in 1 Recovery: 0 in 1 Recovery: 1 in 4 Recove ry : 7 in 7 Recovery: 7 in 7 Recovery: 4 in 4 Recovery: 7 in 7 Recovery: 1 in 1 

### Figure 10-5: DEI30 Values The MSHWG defines in its rep01t " Maximum Allowab le Values" for DEI30 and DE160 in order to address uncertainties ofthe method. The "Maximum All owab le Values for DE130 and DE160 equal 80% ofthe ·'Maximum Never to Exceed Value". As a further coJToboration, the MSHWG utilized the data from the experiment by Dr. Hans C lamann as reported in " An Analysis ofthe Oxygen Protection Problem at Flight Altitudes Between 40 ,000 and 50,000 Feet, Final Report", prepared for the Federal Aviation Agency , Contract FA-955, by Blockley and Hanifan , February 20, 1961 (Reference [6]). Dr C lamann utilized a chamber to si mul ate a rapid decompression from 9,800 feet to 49,200 feet (pressure altitude) and then re-pressurised the chamber at a rate of 410 feet per second (s imul ating an airp lane rate-of-descent). He did not use supp lemental oxygen but breathed air at the chamber pressure . It 

### was rep01ted that he retained consciousness during the entire, albeit short, event. The resu lting integral for this exposure was 12 15 mmHg-sec and sub

stantiates Dr C lamann's statement that consciousness was maintained throughout the decompression. 

### 11. DEl METHOD APPLIED TO A320 NEO AND COMPARISON WITH FAA INTERIM POLICY ON HIGH ALTITUDE CABIN DECOMPRESSION Figure 2-4 and 2-6 ofAppendix I show the envelope descent profiles of Section 8 and the corresponding cabin pressure time-history following a sudden cabin depressurisation caused by an A 3 

### hole in the pressurized fuselage for an A320 NEO at FL 410 and FL398
. The emergency descent is performed by the autopilot, which is triggered 17 seconds after the "Excessive Cabin Altitude" (ExCabAit) warning appears. The 17 seconds include crew recognition time for decompression , oxygen mask donning time and the triggering of the autopilot. The value of 17 seconds is provided in the AC 25-20 and has been confirmed by the MSHWG
.For the envelope profile the Depressurisation Exposure Integral (DEl) was calculated according to the method recommended by the MSHWG
. From Appendix I, Figure 2-4 and 2-6 respectively Figure 2-5 and Figure 2-7 , the following is concluded: For the worst case anticipated geometrical hole size ofA3,
• the exposure of aircraft occupants to cabin pressure altitudes in excess of40000 ft (but below 41000 ft) is less than I minute which is in line with the FAA Interim Policy on high altitude decompression

• the exposure of aircraft occupants to cabin pressure altitudes in excess of 25000 ft is less than 3 minutes which is in line with the FAA Interim Policy on high altitude decompression

• the exposure of aircraft occupants to cabin pressure altitudes in excess of I0000 ft is less than 6 minutes which is in line with the FAA Interim Policy on high altitude decompression

• the Decompression Exposure Integral (DEI) values stay well below the limits recommended by the MSHWG* (see Figure 2-5 and Figure 2-7) * MSHWG recommendation (DEI30: 2 , 160 mmHg-sec , DEI60: 12 ,000 mmHg-sec)

### 12. PUBLIC INTEREST The A320 NEO family of aircrafts is unmodified with respect to the cabin pressure control system , which allows excluding structure and systems failure events of FAR 25.841 (a), Amendment 87 , and would limit compliance demonstration to the narrow exemption requested herein. The exemption requested herein will not adversely affect safety to the occupants and it should be noted that the FAA interim policy , submitted with reference ANM-03-112-16 , dated March 24,2006 would be fully met with the new type of A320 NEO engines and the existing unmodified cabin pressure controls system. Authorization for flight at 41 ,000 feet will enable the A320 NEO family of aircrafts to compete fairly with other existing aircraft that are subject to older amendments without causing any adverse effects on passengers . Approval for flight up to 41,000 feet will:

• Enable this new aircraft to fly at FL41 0, creating more additional lines of aircraft separation in USA airspace without adversely affecting the safety ofthe passengers.
• Enable the Airbus A320 NEO family of aircrafts to compete fairly with other existing aircraft that are not subject to this amendment without causing any adverse effects to the passengers.
• Serve the public interest via the use ofthe newest generation engines in the market, as they offer lower operational cost and higher fuel efficiency. Airplane manufacturers and suppliers will benefit from a granted exemption.
• They will benefit from a competitive aircraft able to find its market. More efficient airplanes that will give continuity to their business.
• Their employees will benefit by sustained employment in the airplane manufacturing industry
. • The public will benefit due to the availability in the future of newer, more efficient airplanes with the possibility of less expensive fares (higher altitudes means less fuel consumption).
• Newer airplanes should also be more reliable reducing the inconvenience of delays and flight cancellations to the public. Finally, there is a benefit to the public in that newer, more efficient airplanes flying at higher altitudes will burn less fuel with coJTesponding fewer emissions of harmful gases and particulates, and the airspace will be more effectively utilized
. Airplanes not certificated under the FAR would be able to achieve lower operating costs because they could be designed to higher maximum certified altitude
. This may give a competitive advantage to non-FAA cettificated airplanes, thus promoting a non-level playing field.

### REFERENCE DOCUMENTS
[I] "Factors Influencing the Time of Safe Consciousness (TSU) for Commercial Jet Passengers Following Cabin Decompression" by Dr. James Gaume, Aerospace Medicine, April 1970
. [2] "Sudden High Altitude Cabin Decompression Immediately Threatens Safety of Aircraft Crew and Passengers" by Dr Stanley Mohler, Flight Safety Foundation , Human Factors 

### & Aviation Medicine, December 1994
. [3] "Concepts Providing for Physiological Protection After Aircraft Cabin Decompression in the Altitude Range of 60,000 to 80,000 Feet above Sea Level", Robet1 P. Gamer, DOT/FAAIAM-99/4, Office ofAviation Medicine, February , 1999. [4] "Neurological Study of Simulated Decompression in Supersonic Transport Aircraft" , Aerospace Medicine, J.B. Brierley and A.N. Nicholson , August 1969. [5] "Neurological Sequelae of Prolonged Decompression" , Aerospace Medicine, A
.N. Nicholson and J.R
. Ernsting, April 1967
. [6] "An Analysis ofthe Oxygen Protection Problem at Flight Altitudes between 40 ,000 and 50,000 Feet, Final Report", prepared for the Federal Aviation Agency , Contract FA-955 , by Blockley and Hanifan, February 20, 1961. [7] "Fundamentals ofAerospace Medicine", Roy 

### L. DeHart, second edition, Williams 

### & Wilkons , 1996, Table 5.12, Respiratory Gas Pressures and Gas Exchange Ratios , pg 91. [8] "Prevention of Hypoxia- Acceptable Compromises" , Aviatim, Space, and Environmental Medicine, J. Ernsting, March 1978
. [9] "A Behavioural and Neuropathological Study ofthe Sequelae of Profound Hypoxia" , A.N. Nicholson, Susan A. Freeland, and J.B. Brierley" , Brain Research , 22 (1970) 327-345. [I 0] "Hypoxia and Performance Decrement" , William F. O'Connor, Ph
. D. , Jim Scow, M.D. , George Pendergrass , Capt., USAF, DOT/FAA/AM 66-15 , May , 1966. [I I] "Performance ofa Continuous Flow Passenger Oxygen Mask at an Altitude of40,000 Feet" , Robert P. Gamer, DOT /FAA/AM-96/4, February 1996
. [ 12] "Rapid Decompression of a Transpot1 Aircraft Cabin : Protection Against Hypoxia" , H. Marotte, C.Toure, J.M
. Clere, and H
. Vieillefond, Aviation , Space and Env. Medicine, Jan. 1990
. [13] "Effects of Decompression on Operator Performance" , William F. O'Connor, Ph. D ., George E. Pendergrass , DOT/FAA/AM 66-10, April, 1966. [14] "Behaviour ofNaive Subjects during Decompress ion : An Evaluation of Automatically Presented Passenger Oxygen Equipment" , Chisholm DM , Billings CE, Bason R, Aerospace Medicine, February I, 1974
. [ 15) "Physiologically Tolerable Decompression Profiles for Supersonic Transport Type Certification", Stanley R. Mohler M.D. and P
.V
. Siegel M
.D., DOT/FAA/AM 70-12 , July 1970. [16] "SAE AIR 4770- Rep011 by the Committee on Uncontained Turbine Engine Rotor Events"

- Data period 1984 through 1989, Aerospace Information Report, 8 April 1996[ 17] AC 20-128A

- "Design Considerations for Minimizing Hazards caused by Uncontained Turbine Engine and Auxiliary Power Unit Rotor Failure" , Advisory Circular- FAA, 1997 [ 18] AC 25-20

- "Pressurization, Ventilation and Oxygen Systems Assessment for Supersonic Flight including High Altitude Operation" , Advisory Circular- FAA, 1996 [ 19] ANM-03-112-16

- "Interim Policy on High Altitude Cabin Decompression (Reference Amendment 87)" , Memo No. ANM-03-112-16, FAA, March 24, 2006 [20] AlA Committee Repot1 on "High Bypass Ratio Turbine Engine Uncontained Rotor Events 1969

- 2006 And Small Fragment Threat Characterization", Volume I, January 20 I0
.