~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 Operations GmbH 

P.O. Box9501 09, 21111 Hamburg, Germany 

Offices: Kreetslag 10, 21129 Hamburg, 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, Chairman & 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 of the 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 req uirements applied by FAA that compliance with 14 CFR 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 

14CFR25.841 (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 control 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 1 I 

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 25-87 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 li kelihood that, if a person is exposed to high-altitude cabin 

pressure from any fai lure not shown to be extremely improbable, 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 of this 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 of fatalities 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 aiming 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 ly 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 pol icy [ 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. I 0228 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 of engines 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 of the 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 basis for these risk assessments as described in the available physiological 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 

of this exemption. 

For such rare UERF scenarios, the FAA has published a policy [19], titled ,Interim Policy on High 

Altitude Cabin Decompression (Reference Amendment 25-87)' , which provides from a safety point of 

view acceptable exposure time limits for high-altitude cabin decompressions 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 il ure 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 decompressions 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 of this petition for exemption) 

5. REASONS FOR REQUESTING EXERCISE OF THE PRIVILEGES OF THE 

EXEMPTION OUTSIDE THE UNITED STATES 

The exemption sought pe1iains to design requirements of 14 CFR 25. If granted, the exemption wi ll 

resu lt in an FAA certificated aircraft design that embodies the privileges of the exemption, and the 

operation of these aircraft will include flights outside the United States. Exercise of the privileges of 

the exemption outside the United States is therefore required. The exemption requested does not involve a specific ICAO standard, and a filing of a difference with ICAO would not be required. 

6. SUPPORTING INFORMATION 

6.1 TEXT OF FAR 25.841 (A), AT AMENDMENT 87 

The fo llowing 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 a ll system and structural failure events, due to the incorporation of new engines with higher bypass ratios and larger fan diameters there are some decompressions 

caused by UERF events for which A320 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 those 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 of Appendix 1). 

The cun·ent regul atory requirements as contained in FAR 25.841 Pressurized Cabin at Amendment 25-

87 states, 

(a) Pressurized cabins and compartments to be occupied must be equipped to provide a cabin 

pressure altitude of not more than 8, OOOfeet at the maximum operating altitude of the airplane 

under normal operating conditions. 

(/)If certification for operation over 25,000 feet is requested, the airplane must be designed 

so that occupants will not be exposed to cabin 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 cabin pressure 

altitude that exceeds the following after decompression from any failure condition not shown 

to be extremely improbable: 

(i) Twenty-jive thousand (25, 000) feet for more than 2 minutes; or 

(ii) F arty thousand (40,000) feet for any duration. 

(3) Fuselage structure. engine and system failures are to be considered in evaluating the cabin 

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 I 0 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 I 0 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 otherwise mitigated. In anticipation of this 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 of the MSH WG to 

show that, assuming a worst case depressurisation event, physiological effects to the aircraft occupants 

stay well within the recommended limits of the MSHWG (see Section 10 of this 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 of time 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 of this 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 stability and airplane performance, this feature exposes a large area to potential penetration 

of the 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 design 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 of rotor 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 

of time to descent to FL250 and FL I 00 is shown in Appendix I, Figure 2-3. This envelops the descent 

performance of A319 and A321 NEO variants for both, ceiling altitudes of 41 ,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 of the 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 

shark let 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 I O,OOOft is for an A320 NEO that weighs W2***, 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 of weight 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 of Appendix I. 

For holes smaller than A1 the cabin pressure altitude does not exceed 2 minutes above 25,000ft, 

whereas it requires a hole of A2 ** 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 of the 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. A3_cFM = 0.257m2 ** and A3_rw = 0.213m2 **, 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 I OOG-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 of 0.5 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 Depressurisation Exposure Integral method 

(DEI). The method defines the envelope of vulnerability of passengers for permanent physiological 

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 I 0-2). The MSHWG proposed the lung partial pressure of oxygen time integral method to assess 

physiological risk to the occupants and called this measure the Depressurisation Exposure Int egral 

(DEI). 

The integral is based on the period of time 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 I 0,000 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 of the severity of the depressurisation event. 

Figure 2-4 and 2-6 of Appendix I presents the cabin altitude- time history of a depressurization event 

resulting rrom a A3 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. 
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HYPOBARIC CHAMBER EXPERlM£NTS 

Time Variation of Simulated Cabin Altltude 

ntlE{mln) 

Fl G U RE I 0-1: 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 /~ 

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100 200 100 400 500 700 

CABIN PRESSURE (tl'ilnHg) 

FIGURE 10-2: DSI versus cabin pressure 

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I 110 

100 

~ 90 

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TIME(min) 

FIGURE 10-3: Integral - DEI30/DEI60 

Note : The Figure I 0-4 graphica lly depicts the DEI30/DEI60 for an event where the cabin pressure 

reaches 51 ,000 feet pressure a ltitude. 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 of the 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]. 

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HYPOBARIC CHAMBER EXPERIMENTS 

Comparison of DEI60 walues 

25ooo ---···-··-----------------··--------·--------·····----------·-·······-·-·······--·-·--···- ;;;=:;=;===;:;~:;:;===;;=; ···l 

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

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 I 0-4: DEI60 values 
HYPOBARIC CHAMBER EXPERIMENTS 

Comparison of DEIJO walues 

6000 ,... ................................................................ . 

5338 

5000 

4000 

3000 

2000 

1000 

0 

Ni cholson- Nicholson- Brierley- Brierley. Nicholson- Brierl ey. Hans 

Ernsting "'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 macaques 1 human 

Survival: 0 in 1 Survival: 3 in 4 Surviva l: 7 in 1 Survival: 7 in 7 Survival: 4 in 4 Survival: 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 Allowable Va lues" for DEI30 and DE160 in order to 

address uncertainties of the method. The "Maximum Allowab le Values for DE130 and DE160 equal 

80% of the ·'Maximum Never to Exceed Value". 

As a further coJToboration, the MSHWG utilized the data from the experiment by Dr. Hans Clamann 

as reported in "An Analysis of the 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 Clamann utilized a chamber to simul 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 (simulating an airplane 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 substantiates Dr Clamann'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 of Appendix I show the envelope descent profiles of Section 8 and the corresponding cabin pressure time-history following a sudden cabin depressurisation caused by an A3 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 of A3, 

• the exposure of aircraft occupants to cabin pressure altitudes in excess of 40000 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 I 0000 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 of the 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 of the 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 of Aviation 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 of the Oxygen Protection Problem at Flight Altitudes between 40,000 

and 50,000 Feet, Final Report", prepared for the Federal Aviation Agency, Contract 

F A-955, by Block ley and Hanifan, February 20, 1961. 

[7] "Fundamentals of Aerospace 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 of the 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 of a Continuous Flow Passenger Oxygen Mask at an Altitude of 40,000 

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 of Naive Subjects during Decompression: 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 I 0.