RA-13-03728 Enclosure 

Page 1 of 18 

Petition for Exemption from 14 CFR 25.841(a)(2) and 25.841(a)(3) Amendment 25-87 

for Uncontained Engine Failure. 

Name and Address of the Petitioner 

Douglas Lane, Deputy Lead Administrator 

The Boeing Company 

PO Box 3707, M/S 03-56 

Seattle, Washington, 98124 

Section(s) of the Regulation(s) from which Relief is Needed: 

25.841(a)(2) and 25.841(a)(3) With Respect to Uncontained Engine Failures. 

§ 25.841 

(a)(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-five thousand (25,000) feet for more than 2 minutes; or 

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

(a)(3) Fuselage structure, engine and system failures are to be considered in 

evaluating the cabin decompression. 

Extent of Relief Needed and Reason(s) 

Regulation Requires: Relief is Necessary because: 

14 CFR 25.841(a)(2) and 

(a)(3) 

Amendment 25-87 

Compliance to be shown with 

cabin pressure altitude limits for 

uncontained engine failure 

Direct compliance would limit maximum 

aircraft altitude to less than 40,000ft and 

would: 

A) create an economic impact to 

operators associated with higher fuel 

burn 

B) have an environmental impact due to 

increased engine emissions associated 

with higher fuel burn 

C) reduce competitiveness of the 737-7/-

8/-9 in the aircraft marketplace 
RA-13-03728 Enclosure 

Page 2 of 18 

Description of Issue 

The 737-7/-8/-9 aircraft is being designed to operate at a maximum cruise altitude of 41,000 ft. 

Amendment 25-87, Reference (1), established new requirements in § 25.841(a) intended to upgrade 

the airplane and equipment airworthiness standards for subsonic transport airplanes operated above 

40,000 feet. These were based in part on special conditions that had been used on type certification 

of executive business airplanes for many years. Specifically, Amendment 25-87 created three 

requirements in §§ 25.841(a)(2)(i), 25.841(a)(2)(ii), and 25.841(a)(3) governing the cockpit/cabin 

environment: 

§ 25.841(a) subpart; 

(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-five thousand (25,000) feet for more than 2 minutes; or 

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

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

decompression. 

The Boeing Company respectfully submits that compliance with §§ 25.841(a)(2), and 25.841(a)(3) 

as written, with respect only to the consideration of an uncontained engine failure, provides no 

increase in safety with respect to modern transport category jet aircraft when considering the safety 

record of the fleet over the last 53 years. The fleet has a demonstrated safety record with millions of 

hours at altitudes similar to the maximum cruise altitude proposed for the 737-7/-8/-9. Despite the 

improved descent capability of the 737-7/-8/-9 over previously certificated aircraft of similar 

category and class, compliance with 25.841(a)(2)(i) following an uncontained engine failure would 

limit the 737-7/-8/-9 maximum certificated altitude. In addition, The Boeing Company assessment 

of the §25.841(a), Amendment 87, impact on overall fleet safety raised concerns about several 

unintended consequences. One such consequence is higher density air traffic at altitudes below 

40,000 feet as a result of limiting new aircraft with wing mounted engines to altitudes below 40,000 

feet. This may result in additional cost to maintain an adequate level of safety for the air traffic 

system. 

The 737-7/-8/-9 is designed to fly at cruise altitudes that will maximize fuel efficiency. The 

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

25.841(a)(3) for uncontained engine failure would significantly impact the marketability of the 

737-7/-8/-9. This concern is shared by other manufacturers of airplanes with wing-mounted engines 

seeking new or amended Type certification. No transport category airplane with wing-mounted 

engines certificated today for operation above 39,000 feet can meet the new cabin altitude limits 

within the current §§25.841(a)(2) and 25.841(a)(3) without an exemption. 

The 737-7/-8/-9 incorporates new technology, lessons learned from previous and current production 

airplanes, and complies with the latest airworthiness standards (except as noted in 737-7/-8/-9 

Certification Basis) throughout to provide a safer, more efficient transportation option for operators 

and occupants. Grant of this petition provides the public the benefits of the 737-7/-8/-9 airplane. 
RA-13-03728 Enclosure 

Page 3 of 18 

As stated in the Mechanical Systems Harmonization Working Group (MSHWG) report (reference 

(3)), there is an inherent physiological risk to humans when exposed to high cabin altitudes. In the 

737-7/-8/-9 design, The Boeing Company mitigates risk to high cabin altitude exposure by 

reasonable design requirements, proven design methodologies and operational considerations 

regardless of the cause of the decompression event. It is intended that the proposed exemption 

addresses the intended concern for safety without imposing the operational economic penalties 

driven by §§25.841(a)(2) and 25.841(a)(3) as currently written. In the following, The Boeing 

Company provides: 

 a background of the current rule and activities to harmonize it 

 a review of the safety history of high altitude commercial flight 

 a discussion of hypoxia physiology data upon which rulemaking activities are based 

 a discussion of the impact of compliance with uncontained engine rotor burst aspects of the 

existing rule, as related to economics, environmental, and air traffic considerations. 

 proposed risk mitigation 

 statements addressing public interest and no adverse impact to safety. 

Background on 14 CFR § 25.841(a)(2)(3), Amendment 25-87 

Amendment 25-87 to § 25.841(a) was made effective July 5, 1996. The focus of the rule was to 

codify the special conditions formerly used in the certification of high altitude operation, generally 

applied to general aviation and transport category business jets covering operation up to 51,000 feet. 

This section was changed without being harmonized with the Joint Aviation Authorities (JAA) or 

now the European Aviation Safety Agency (EASA). It is noteworthy that the JAA and EASA have 

not adopted the same regulations as levied in 14 CFR §25.841(a) as promulgated in Amendment 

25-87. The JAA INT/POL/25/16, Issue 1, Date: 01.06.03, “Airworthiness Standards for Subsonic 

Transport Aeroplanes to be operated above an altitude of 41,000 ft,” states, with respect to 

evaluation of engine rotor burst, “It is JAA opinion that turbine engine installations failures should 

be assessed against the specific requirement of JAR 25.903(d) and should not be part of the present 

Special Conditions, this is to allow a consistent approach at the aircraft level...” 

The provisions of §§25.841(a)(2) and 25.841(a)(3) of Amendment 25-87 effectively limit new 

transport category airplanes with wing-mounted engines to operating altitudes well below 40,000 

feet. This has major cost impacts since new airplane models may not be able to compete with 

existing certificated airplanes or derivative airplanes, which do not have §25.841(a), Amendment 

25-87 as part of their certification basis. The existing airplanes can cruise at altitudes above 40,000 

feet where they are more fuel-efficient. 

The Aerospace Industries Association (AIA) and European Association of Aerospace 

Industries/Association Européenne des Constructeurs de Matériels Aeronautique (AECMA) 

petitioned the Federal Aviation Administration to amend 14 CFR 25.841(a), Amendment 25-87, 

pressurized cabins, and the associated Advisory Circular 25-20. It was suggested that the proposed 

amendment be addressed through the auspices of the Aviation Rulemaking Advisory Committee 

(ARAC). The petitioners recommended that harmonization with the Joint Airworthiness 
RA-13-03728 Enclosure 

Page 4 of 18 

Requirements and Transport Canada’s standards be accomplished simultaneously through the ARAC 

process. 

The petitioners represented the manufacturers of transport category airplanes in the United States 

and Europe. As such, they have an interest in this rulemaking proposal because new and derivative 

airplanes designed to meet 14 CFR Part 25 as amended at Amendment 25-87 will have significantly 

higher design and operating costs than currently certificated airplanes, with no measurable increase 

in safety. These higher costs impact the ability of manufacturers to develop new airplanes that can 

compete with previously approved airplanes. The petitioners also identified that the economic 

evaluation conducted by the FAA did not consider the costs associated with applying this new 

standard to changes to existing type certificates (derivative models) when assessing the costs and 

benefits accruing from the amendment, nor whether the new requirement itself could be met by any 

practical means for any new or derivative airplane. 

In July 2001, the FAA assigned the ARAC and the Mechanical Systems Harmonization Working 

Group (MSHWG) the task of addressing various concerns with the regulation, raised by industry, 

and of reaching a consensus among medical experts, representatives from the FAA, JAA, Air 

Transport Association (ATA), Airline Pilots Association (ALPA), Association of Flight Attendants 

(AFA) and Aircraft Manufacturers (members with representation in the Aerospace Industries 

Association (AIA), Aerospace and Defense Industries Association of Europe - Standardization (ASD 

STAN) [formerly known as the Association of European Aircraft and Component Manufacturers 

(AECMA)] or the General Aviation Manufacturers Association (GAMA)). The MSHWG agreed 

that the existing standard may be conservative relative to engine related failures when considering 

the associated risks and exposure to safety. The issuance of an FAA Interim Policy, March 2006, 

Reference (2) is consistent with this position, as is the MSHWG working group report, Reference 

(3), which identified the existing requirements as being conservative relative to safety. In 

consideration of comments received on the draft Interim Policy and the acceptance of the MSHWG 

report by Transport Airplane and Engines Issues Group (TAEIG), the FAA worked with 

manufacturers to establish appropriate criteria for 25.841(a) with respect to an uncontained engine 

failure. The following proposal is consistent with those criteria and similar to exemptions granted 

for the 787-8, 747-8, 747-8F, A380, A350-900, ERJ 170, and ERJ 190. 

Safety History 

The original 14 CFR §§25.841(a)(2) and 25.841(a)(3) had the goal of ensuring that no fatalities or 

permanent physiological harm occurred following a rapid depressurization event. However, the 

MSHWG believed that there is an inherent risk to occupant health and safety associated with any 

rapid depressurization event. The MSHWG concluded that all occupants are at some level of risk 

during a decompression event and the resulting emergency descent, flight, and landing. Fatalities 

may occur during the initial event (i.e., from impact of uncontained engine debris or from being 

ejected from the airplane). In addition, some cases of permanent physiological harm could result 

from hypoxia among those occupants at increased risk due to pre-existing health factors (e.g., age, 

chronic and acute medical conditions, etc.). The following is presented to establish that the 

demonstrated risk to safety due to rapid depressurizations is non-significant when compared to other 

risks to safety. 
RA-13-03728 Enclosure 

Page 5 of 18 

Previously certificated large transport aircraft incorporating established design practices have safely 

operated at altitudes in excess of 40,000 feet for more than 30 years, representing many millions of 

flight hours. Historically, relatively few accidents or incidents have occurred during cruise. 

According to the statistics, for the period 1959 - 1996, only 6.8 percent of accidents in the worldwide 

commercial fleet history have occurred during cruise; even though the highest percentage of the 

flight time (57%) is at cruise (Reference (4)). See Figure 1-1. More recent statistics, show only 6.0 

percent of accidents have occurred during cruise for the period 1994 - 2003, (Reference (5)) and 11 

percent of accidents have occurred during cruise for the period 2002 – 2011 (Reference (16)). See 

Figure 1-2 and 1-3 respectively. 

Figure 1-1, Fatalities, Worldwide Commercial Jet Fleet – 1959 - 1996 

 
RA-13-03728 Enclosure 

Page 6 of 18 

Figure 1-2, Fatalities, Worldwide Commercial Jet Fleet – 1994 - 2003 

Accidents and Onboard Fatalities by Phase of Flight

Hull Loss and/or Fatal Accidents - Worldwide Commercial Jet Fleet - 1994 - 2003

Hull loss and/or fatal accidents Onboard fatalities

Taxi, load,

parked

Takeoff Initial

climb

Climb

Fatlies

Cruise Descent Initial

approach

Final

approach

Landing

11

3

25

Hull

loss

and/or

fatal

accidents 539

11

17

1,619

788

13 7

14

1,066

13

Initial

approach

7%

13%

12%

Descent

3%

8%

11%

Final

approach

6%

16%

3%

Percentage of accidents/fatalities

Takeoff

12%

8%

1%

Initial

climb

5%

14%

1%

Landing

45%

2%

1%

Taxi,

load,

parked

5%

0%

Climb

(flaps up)

8%

25%

14%

Cruise

6%

12%

57%

17% 51%

22% 18%

Accidents

Fatalities

Initial

approach fix

Exposure = percentage of flight time

based on flight duration of 1.5 hours

Distribution of accidents and fatalities

0

20

40

60

80

100

0

500

1000

1500

2000

902

541

93

161

Fatalities

865

Final

approach fix

16

2003 STATISTICAL SUMMARY, MAY 2004
RA-13-03728 Enclosure 

Page 7 of 18 

Figure 1-3, Fatalities, Worldwide Commercial Jet Fleet – 2002 - 2011 

Figure 2 shows fatal accidents by category for the world commercial jet fleet for the period of 1992 

to 2001. Note for this period, of the 7,171 fatalities from all causes, none were due to hypoxia 

resulting from in-flight rapid decompression events at altitudes greater than 25,000 feet. Relative to 

other causes, decompressions resulting in hypoxic fatalities are not a significant accident contributor. 
RA-13-03728 Enclosure 

Page 8 of 18 

Figure 2: Fatal Accidents by Category 

Additionally, an assessment of decompressions since the 2001 completion of the above study 

through 2011, confirmed there were no additional fatalities due to hypoxia resulting from in-flight 

rapid decompression. There were 121 additional fatalities related to hypoxia from a single event; 

the Helios Airways Flight HCY522 accident which was not a decompression event, but a failure of 

the flight crew to properly configure the pressurization system and a subsequent failure to recognize 

that the aircraft was not pressurized after takeoff, Reference (15). There were no additional deaths or 

injuries resulting in permanent physiological harm and only two additional incidents were recorded 

as having resulted in minor barotrauma injuries. 

It should also be noted that very few rapid decompression events, if any, have exposed aircraft 

occupants to cabin pressure altitude profiles that run the risk of permanent harm to occupants. 

Industry experience shows that very few cases of decompressions at high altitude resulting in death 

or permanent physiological harm have occurred. The FAA cited 3 cases as examples of uncontained 

engine failure for consideration. In one case, a DC-10 (cruise flight near Albuquerque, New 

Mexico) reported several cases of initial decompression sickness apparently with no permanent 

injuries. However, it was noted that 24 passengers and crewmembers were brought to the hospital at 

Kirtland AFB for treatment of symptoms including, barotraumas (ear problems), minor abrasions, 

and smoke inhalation. Because there was no known follow-up on these occupants, there is no way 

to assess the extent of physiological injuries sustained during this decompression event. The NTSB 

report, (Reference (6), NTSB report NTSB-AAR-75-2) concluded that the rotor burst occurred due 

to the fact that “The flight crew (was), in effect, performing an untested failure analyses on the auto 

throttle system.” In the second case (Sioux City, Iowa), the aircraft damage was aft of the pressure 

bulkhead, thus no rapid decompression occurred. The FAA cites this event to estimate the damage if 

the debris field had been forward of the pressure bulkhead. In the third case (Pensacola, Florida), the 

airplane was performing a takeoff (not cruise) when the event occurred and the flight deck crew 

successfully performed a rejected takeoff. Thus, this case did not encounter a rapid decompression. 

It should be noted that the FAA cited these three cases (Reference (7)) because they were “data rich” 

Fatalities by Accident Categories 

Fatal Accidents - World Commercial Jet Fleet - 1992 Through 2001

0

500

1,000

1,500

2,000

2,500

Lost control

CFIT

Midair collision

In-flight fire

Fuel tank

Landing

Takeoff config

Rwy incursion

Ice/snow

Windshear

Misc. fatality

Fuel exhaust

RTO

Turbulence

Decompression

Unknown

Fatalities

Total fatalities 2001 fatalities

Sources: Boeing Airplane Safety Engineering (ASE) and Safety Information System (SIS), National Transportation Safety Board (NTSB)

Decompression

(Hypoxia) >25Kft
RA-13-03728 Enclosure 

Page 9 of 18 

events. In addition to the “data rich” events discussed above, there have been nine other uncontained 

engine failures at cruise identified to the FAA, Reference (8), however, none of these other events 

caused a cabin decompression. 

The events experienced to date as discussed above were associated with 1st generation engine 

technology. Safety enhancement initiatives with respect to critical rotating parts (inspecting for 

cracks in disks and using continually updated maintenance data to refine disk inspection criteria), as 

well as improvement in engine technology, lessons learned, and 2nd /3rd generation engine design 

practices have resulted in a reduction in uncontained engine failure events. The uncontained engine 

failure rates of 2nd/3rd generation engines compared to 1st generation engines has improved by 

approximately 95% based on historical Boeing data on uncontained engine failures. 

As noted previously regarding the three “data rich events” (the Albuquerque, Sioux City, and 

Pensacola events), only the Albuquerque event resulted in a decompression. Furthermore, the 

Albuquerque event remains an inappropriate event as a “decompression” model, particularly since 

the NTSB noted that “The flight crew was, in effect, performing an untested failure analyses on the 

autothrottle system” prior to the engine failure, Reference (6), NTSB report NTSB-AAR-75-2. 

Figure 3 depicts pressurization events by cause. Note that uncontained engine failure is an 

insignificant contributor to the total number of events. 

Figure 3: Pressurization Events by Cause per Flight Hour 

In conjunction with the above data, it should be noted that very few decompression events exposed 

the aircraft occupants to cabin pressure altitude profiles which run the risk of permanent 

physiological harm. Figure 4 summarizes significant transport category decompression events 

Decompression Events by Cause

Pressurization Events per Hour and per Flight, by Cause

0.00E+00

5.00E-07

1.00E-06

1.50E-06

2.00E-06

2.50E-06

3.00E-06

3.50E-06

4.00E-06

Unknown

Press. Sys. 

Door/Seal

Structural

Procedural

Engine

Shootdown/Bomb

# Ev/Hr # Ev/Flt

Sources: Boeing Airplane Safety Engineering (ASE) and Safety Information System (SIS), National Transportation Safety Board (NTSB)

Engine

Engine Events Are Rare Contributors To Decompression Events
RA-13-03728 Enclosure 

Page 10 of 18 

resulting in fatalities or incapacitation. Note that while fatalities were incurred, none would have 

been prevented by the intent of § 25.841(a), Amendment 25-87 which was promulgated in large part 

to prevent death or permanent physiological harm from hypoxia as a result of a rapid decompression 

caused by a large hole in the pressure vessel from an uncontained engine failure. The only fatal 

event since this data was taken has been the previously discussed Helios event.

Figure 4: Pressurization Events with Fatality, Incapacitation or Injury 

Notes: Total of 2866 pressurization events reported 1959-2001. Transport Category 

Airplanes over 60,000 lbs. Event Altitude and Cabin Altitude were reported for 

873 events. 

Sources: Boeing Airplane Safety Engineering (ASE) and Safety Information System (SIS), 

National Transportation Safety Board (NTSB) 

Of the 18 events that resulted in fatalities, 10 events were at cabin altitude exposures less than those 

altitudes addressed by § 25.841(a)(2), Amendment 25-87. In four of the remaining eight events, 

fatalities were due to injury directly attributed to the event rather than from hypoxia (one 

catastrophic structure loss, two engine failures, and one wheel burst). The remaining four events 

were attributed to crew error, un-annunciated loss of pressurization, and oxygen system failure. 

Current generation aircraft, (1980s through 2000s) introduced higher performance permitting higher 

altitude flight in response to the need for increased fuel efficiency and avoidance of increasingly 

crowded airspace at altitudes below 40,000 feet. The MSHWG report, Reference (3) concluded for 

the world commercial jet fleet for the period of 1992 to 2001, no hypoxia related fatalities were due 

to in-flight decompression events. This safety record has been maintained even as newer airplanes 

fly at these higher altitudes more often than older airplanes (see Figure 5). As stated previously, an 

assessment of decompressions since the 2001 completion of the above study through 2011 

confirmed there were no additional fatalities or permanent physiological harm due to hypoxia 

All Pressurization Events with associated

Fatality, Incapacitation or Injury 

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 45,000 50,000

Event Altitude

Maximum Cabin Altitude

Fatality/Incapacitation Injury

All Pressurization Events with associated

Fatality, Incapacitation or Injury 

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 45,000 50,000

Event Altitude

Maximum Cabin Altitude

Fatality/Incapacitation Injury
RA-13-03728 Enclosure 

Page 11 of 18 

resulting from in-flight rapid decompression, and only two additional incidents resulting in minor 

barotrauma injuries. As discussed previously, the Helios Airways Flight HCY522 accident was not 

a decompression event, but a failure of the flight crew to properly configure the pressurization 

system and a subsequent failure to recognize that the aircraft was not pressurized after takeoff. 

Based on these facts, the MSHWG report conclusions remain valid. Three separate studies have 

recently been made to illustrate the extent of air traffic operations at high altitude in today’s air 

traffic system. While today’s numbers are significant, the new generation of airplanes similar to the 

737-7/-8/-9 are being designed to cruise at altitudes above 37,000 feet for even longer portions of 

their mission. 

Figure 5: Frequency of Flights above 37,000 ft. and 40,000 ft. Altitude of New Design Aircraft 

vs. Older Design Aircraft. 

Aerospace Hypoxia Physiology Data 

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

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

observations made from flight physiological and medical experiments. The cabin altitude limits in 

Amendment 25-87 were developed by the FAA based in part on recommendations from the FAA’s 

Civil Aeromedical Institute (CAMI), which were based on the concept of “Time of Safe 

Unconsciousness” (TSU) documented by James G. Gaume in his 1970 paper (reference (9)). The 

study concluded with the statement that, “... a plea must be made for collection of better data.” 

Gaume’s 1970 paper is only one source in establishing safety basis. It should be understood that the 

proposed TSU criteria was established as a compensating consideration to the elimination of the 

Altitude Reports By Airplane Model

FAA’s Enhanced Traffic Management System (ETMS) Reports for U.S.

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

707

DC-8

727

DC-9/717

737747

DC-10

A300

MD-80

767757

A310A320

MD-11

A340

A330

777

A319

737NG

Reports

Above 40,000 ft

Above 37,000 ft

First Flight of Type Prior to 1980

Commercial Aircraft above 28,000 feet

• Data represents reports from one week in Sept. 2000

• Based on position reports every 3 minutes.
RA-13-03728 Enclosure 

Page 12 of 18 

passenger oxygen system. Today’s commercial transport are required to provide an emergency 

oxygen system providing additional margin of safety. 

The MSHWG agreed additional data based on further study would benefit the establishment of new 

standards. In lieu of new data the MSHWG established physiological exposure limits that are 

conservative with respect to the data available. The MSHWG considered the available physiological 

exposure research which included several papers that have been circulated in the aerospace medical 

community, all with the objective of establishing physiological limits to occupants following cabin 

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

exposure that the MSHWG documented its recommendations in the Reference (3) TAEIG accepted 

report. The following are summaries of the reports from recognized Aerospace Medical Doctors 

addressing physiological information that was considered by the MSHWG: 

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

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

adequate recovery of unconscious passengers without any supplemental emergency 

oxygen to the occupants, with an aircraft emergency descent of 6200 feet per minute and 

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

considered acceptable. Reference (9): “Factors Influencing the Time of Safe Unconsciousness (TSU) for Commercial Jet Passengers Following Cabin Decompression” 

by James Gaume, Aerospace Medicine, April 1970. 

 Dr. Stanley R. Mohler, a former director of CAMI (FAA’s Civil Aeromedical Institute), 

analyzed a number of actual decompression cases, including data from studies by Barron, 

Reference (10), and Gaume. He concluded that brain damage in the absence of oxygen 

starts after about four minutes, and that three minutes above 25,000 feet is a reasonable 

limit to protect against permanent physiological damage from a cabin decompression 

occurring at up to 45,000 feet. Reference (11): “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. 

 Dr. Robert Garner, Research Physiologist, Protection and Survival Laboratory at CAMI, 

agrees that limiting cabin altitude exposure to 25,000 feet for up to three minutes and 

never allowing it to exceed 45,000 feet would provide an acceptable level of safety. His 

views on this matter have been communicated to the FAA Transport Standards Staff. 

 Draft White paper issued by CAMI - FAA Civil Aerospace Medical Altitude Rule: 

presented in the MSHWG in July 2002, Reference (12), Page 13, states that exposure: if 

unprotected, passengers to a 41,000 feet altitude would be approximately equal to 

exposure at a 40,000 feet altitude. 

 “Neurological Study of Simulated Decompression in Supersonic Transport Aircraft,” 

Aerospace Medicine, J.B. Brierley and A. N. Nicholson, August, 1969, Reference (13), 

concluded that cabin altitude exposure above 10,000 feet not more than eight minutes up 

to peak of 36,000 feet does not cause brain damage. 
RA-13-03728 Enclosure 

Page 13 of 18 

 “Neurological Sequelae of Prolonged Decompression,” Aerospace Medicine, A. N.

Nicholson and J.R. Ernsting, April 1967, Reference (14) concluded that cabin altitude 

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

damage. 

In consideration of the above studies, comments received on the draft Interim Policy, and the 

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

§25.841(a) with respect to an uncontained engine failure. These criteria are more conservative than 

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

criteria as presented in the Proposed Risk Mitigation discussion provided later in this petition. 

Impacts of Compliance with the Uncontained Engine Failure Aspect of Rule 

The Boeing Company’s 737-7/-8/-9 will fully comply with the latest airworthiness standards (except 

as noted in the 737-7/-8/-9 Certification Basis) including §§25.841(a)(2) and 25.841(a)(3), 

Amendment 25-87, except as related to specific structural failure event as defined in 737-7/-8/-9 

Certification Basis exception, and as related to an uncontained engine failure event as defined herein. 

With respect to uncontained engine failure events, the impact of § 25.841(a), Amendment 25-87 to the 

aviation industry and the flying public is significant. The “impact” of compliance takes three forms (1) 

economic which lead to (2) reduced potential for overall safety improvements and (3) environmental. 

(1) While it is difficult to place an exact dollar amount on the impact of these new requirements 

on the 737-7/-8/-9, it is clear that not granting the proposed exemption would have severe impact. 

This conclusion is based on the reduction in maximum cruise altitude that compliance with 

§§ 25.841(a)(2) and 25.841(a)(3), Amendment 25-87 as it relates to uncontained engine failure 

would result in. This reduction in maximum cruise altitude would result in significantly higher 

operating costs, based on the significant increased fuel burn due to operations at altitudes not 

optimum for these airplanes. These higher costs will adversely impact the ability of the Boeing 

737-7/-8/-9 to compete with previously certificated airplanes which can operate at the more 

economical cruise altitudes typically in excess of 37,000 feet. In addition, restricting airplane 

operations to lower altitudes will increase traffic congestion. Three separate studies have shown 

that the number of operations above 37,000 feet are significant today and the trend is for newer 

airplanes to cruise at these altitudes for even longer portions of their mission. Limiting operation 

of new generation airplanes to lower altitudes will result in higher traffic density, which in turn 

will result in higher cost of safety in order to maintain established air traffic vertical and 

horizontal separation requirements. 

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

released. Each of these amendments has the intent of an increase in aviation safety. The Boeing 

737-7/-8/-9 will meet the latest amendments in effect at the time of application, except as noted 

in the 737-7/-8/-9 Certification Basis. The net result is that the 737-7/-8/-9 incorporates the safety 

advancements as intended within these later amendments. Any significant impact to the 

marketability of the 737-7/-8/-9 will, at a minimum, result in a reduced number of aircraft with 
RA-13-03728 Enclosure 

Page 14 of 18 

this higher level of safety as compared with the previous generation of aircraft, or at a maximum, 

preclude the manufacture of this new model series of aircraft. In either case, Amendment 25-87 

results in a reduced potential for overall aviation safety improvements. 

(3) As stated in (1) above, the restriction to maximum cruise altitude imposed upon the 

737-7/-8/-9 due to compliance with §§ 25.841(a)(2) and 25.841(a)(3), Amendment 25-87 as it 

relates to uncontained engine failure has a significant adverse impact on 737-7/-8/-9 fuel burn. 

This additional fuel burn not only increases 737-7/-8/-9 operating costs, but will also increase 

engine emissions (e.g. CO2).

Proposed Risk Mitigation 

It is The Boeing Company’s assessment that the risk to safety which is attempted to be mitigated by 

the new rule §§ 25.841(a)(2) and 25.841(a)(3), creates unintended consequences. The existing fleet 

has demonstrated safe operations via millions of hours of flight at altitudes similar to those proposed 

for the 737-7/-8/-9. The risk of rapid depressurization following an uncontained engine failure is 

better mitigated by a combination of proven design practices established through years of airplane 

industry experience combined with today’s improved technical capabilities. It is intended that the 

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

for safety without the non-commensurate impacts driven by current requirements of §§25.841(a)(2) 

and 25.841(a)(3). 

It must be reiterated that this request for exemption for §§25.841(a)(2) and 25.841(a)(3) is limited to 

only uncontained engine failures. For rapid depressurization caused by system failures, 

§§25.841(a)(2) and 25.841(a)(3) will be complied with as amended by Amendment 25-87. For some 

specific structural failures §§25.841(a)(2) and 25.841(a)(3) at Amendment 25-87 will be complied 

with as modified by exception recorded in the 737-7/-8/-9 Certification Basis. All mechanical 

and/or functional interfaces that could potentially violate the physiological limits imposed by 

§25.841 (a) are considered. Robust structural and systems design, and the ability for the airplane to 

rapidly descend, are key to assuring the safety of airplane occupants and are an inherent part of the 

737-7/-8/-9 design. The Boeing Company design practices refine the requirements into subrequirements for systems, structures, aerodynamics, and performance in order to assure airplane 

level compliance. 

A key factor in ensuring occupant survivability, after an Uncontained Engine Failure causes a 

depressurization, is the aircraft descent performance. The 737-7/-8/-9 spoiler system is changed to 

employ greater speedbrake deployment for rapid decompression conditions than for normal in-flight 

operations. Also, the Flight Control Computer (FCC) Level Change mode is changed to be more 

aggressive controlling the target speed during emergency descent. Both changes will improve the 

737-7/-8/-9 descent capability compared to the 737-700/800/900 airplanes. 

The following more specifically addresses The Boeing Company proposed means of compliance for 

rapid depressurizations related to uncontained engine failures. Using the FAA established criteria 

(Reference (2)), The Boeing Company proposes to mitigate the risk to occupants from exposure to 
RA-13-03728 Enclosure 

Page 15 of 18 

high cabin altitudes resulting from uncontained engine failure, in part, by implementing the 

following design requirements on the 737-7/-8/-9 airplane: 

 Design Requirement 

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

altitude that exceeds the following after decompression from any engine failure condition 

not shown to be extremely improbable: 

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

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

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

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

In calculating the descent capability of the airplane in order to meet the cabin altitude requirements, 

the loss of the failed engine’s contribution as a source of power to the systems enabling the descent 

need be considered. (i.e. If losing power on one engine results in loss of a hydraulic system, and that 

in turn reduces the number of spoilers that are available, the descent rate must be based on the 

capabilities of the degraded system.) Systems degradation due to debris damage from an 

Uncontained Engine Failure need not be considered. 

Statement of Public Interest 

The Boeing Company Model 737-7/-8/-9 will comply with the latest airworthiness standards (except 

as noted in 737-7/-8/-9 Certification Basis) including §§25.841(a)(2) and 25.841(a)(3), Amendment 

25-87, except as related to specific structural failure event as defined in 737-7/-8/-9 Certification 

Basis exception, and as related to an uncontained engine failure event as defined herein. Specific 

features of the 737-7/-8/-9 design mitigate the safety risk to occupants due to a decompression 

resulting from an uncontained engine failure. Improvements in engine technology, application of 

lessons learned, and 2nd /3rd generation engine design practices have resulted in a reduction in 

uncontained engine failure events and the risk of a rapid depressurization. As stated above, the 

Boeing 737-7/-8/-9 will meet all the latest amendments in effect at the time of application, except as 

noted in the 737-7/-8/-9 Certification Basis. The net result is that the 737-7/-8/-9 incorporates the 

safety advancements as intended within these later amendments. 

In addition, the 737-7/-8/-9 will provide improved operating economics, and environmental 

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

safety relative to previously certificated airplanes, while reducing operational costs by reducing the 

amount of fuel consumed. The cost of maintaining the level of safety within the existing air traffic 

management system will not be adversely impacted by continuing to allow operation in the less 

congested altitudes typically well above 37,000 feet. The reduction in fuel consumed will also result 

in reduced emissions. These benefits will accrue with no decrease in safety. 

Statement of No Adverse Effect on Safety 
RA-13-03728 Enclosure 

Page 16 of 18 

The exemption requested will not adversely affect safety. As previously discussed, the 737-7/-8/-9 

will comply with §25.841(a) in other aspects of a rapid depressurization, except as related to specific 

structural failure event as defined in 737-7/-8/-9 Certification Basis exception, and as related to an 

uncontained engine failure event as defined herein. In the unlikely event of an uncontained engine 

failure, the 737-7/-8/-9 design incorporates a high level of safety due to its descent capability and 

other design features. As concluded herein, and based on the MSHWG report (reference (3)), and 

the Interim Policy (reference (2)), the world commercial jet fleet has had no hypoxia related fatalities 

due to in-flight decompression events caused by an uncontained engine failure. This safety record 

has been maintained even as newer airplanes fly at higher altitudes more often than older airplanes. 

In keeping with time-above-altitude FAA guidance and the recommendations of the MSHWG 

report, as adopted by TAIEG, Boeing has incorporated design features that appropriately address the 

risk to safety following an uncontained engine failure. Therefore, granting of the exemption will not 

compromise safety to the airplane occupants. 

Summary to be Published in the Federal Register 

PETITIONER: Boeing Commercial Airplanes 

SECTION OF 14 CFR AFFECTED: 14 CFR 25.841(a)(2)(3) 

DESCRIPTION OF RELIEF SOUGHT: To allow relief from the requirements pertaining to 

cabin decompression following certain extremely rare uncontained engine failures for the 

Boeing Model 737-7/-8/-9. 

Request to “Waive Publication and Comment” 

Boeing requests to waive the requirement for publication and comments based on similar 

exemptions granted to the following aircraft: 787-8, 747-8, 747-8F, A380, A350-900, ERJ 170 and 

ERJ 190. 

Privileges of the Exemption Outside of the United States 

Per § 11.81(h), Boeing requests that the privileges of this exemption be extended outside the United 

States. This extension of privileges is necessary for operations based within foreign countries 

having bilateral agreements with the United States accepting FAA 14 CFR part 25 as their 

airworthiness standards for transport category aircraft. The 737-7/-8/-9 is intended for the global 

market place. 

Conclusion 
RA-13-03728 Enclosure 

Page 17 of 18 

The information in this petition for exemption provides evidence that compliance with §§ 

25.841(a)(2), and 25.841(a)(3), with respect to an uncontained engine failure, provides no increase in 

safety. The 737-7/-8/-9 provides advancements in technology and safety relative to previously 

certified aircraft. Grant of this petition provides the public the benefits of the 737-7/-8/-9 airplane. 

Operators will be able to operate the 737-7/-8/-9 where it is most efficient and therefore will not face 

higher operating costs due to increased fuel burn. Furthermore, reduced fuel burn will lead to lower 

engine emissions resulting in positive impact to the environment. By granting this petition for 

exemption the true benefits of 737-7/-8/-9 will be realized, causing no adverse effect on safety. 

References 

1) Amendment 25-87 Final Rule, Docket 26070, Federal Register Volume 61, Number 109, 

June 5, 1996 

2) FAA Interim Policy, ANM-03-112-16, Subject: Interim Policy on High Altitude Cabin 

Decompression (Reference Amendment 25-87) Issued March 24, 2006 

3) Mechanical Systems Harmonization Working Group (MSHWG) Final Report on FAR 

25.841(a)(2,3), dated August 2003, submitted to FAA October 21, 2003 

4) Statistical Summary of Commercial Jet Airplane Accidents, Worldwide Operations, 

1959-2002, Published by Boeing Commercial Airplane, May, 2003. 

5) Statistical Summary of Commercial Jet Airplane Accidents, Worldwide Operations, 

1959-2003, Published by Boeing Commercial Airplane, May, 2004. 

6) NTSB-AAR-75-2, AIRCRAFT ACCIDENT NATIONAL AIRLINES, INC.,DC-10-10, 

N60NA NEAR ALBUQUERQUE, NEW MEXICO, November 3,1973 

7) Uncontained Engine Failure Fuselage Hole Analysis, Draft Technical Note, October 2001 

8) Uncontained Engine Damage Database, ACCESS 2000 Database, FAA UED v001, June 

10, 2002 

9) Factors influencing the time of Safe Unconsciousness (TSU) for commercial passengers 

Following Cabin Decompression, Gaume, J., 1970. Aerospace Medicine, April 1970, 

pages 382-385 

10) Barron, C. and Cook, T., Effects of Variable Decompressions to 45000 feet, Aerospace 

Medicine, May 1965, pages 425 - 430 

11) Mohler, Dr. Stanley, “Sudden High Altitude Cabin Decompression Immediately 

Threatens Safety of Aircraft Crew and Passengers,” Flight Safety Foundation, Human 

Factors & Aviation Medicine, December 1994 

12) Draft White paper issued by CAMI - FAA Civil Aerospace Medical Altitude Rule: 

presented in the MSHWG in July 2002 

13) “Neurological Study of Simulated Decompression in Supersonic Transport Aircraft,” 

Aerospace Medicine, J.B. Brierley and A.N. Nicholson, August, 1969 

14) “Neurological Sequelae of Prolonged Decompression,” Aerospace Medicine, A.N. 

Nicholson and J.R. Ernsting, April 1967 

15) Hellenic Republic Ministry of Transport & Communications, AAIASB Aircraft Accident 

Report, Helios Airways Flight HCY522, Boeing 737-31S At Grammatiko, Hellas on 14 

August 2005, Dated 11/2006 

16) Statistical Summary of Commercial Jet Airplane Accidents, Worldwide Operations, 

1959-2011, published by Boeing Commercial Airplane, July 2012. 
RA-13-03728 Enclosure 

Page 18 of 18 

17) “Calculation of Flow of Air and Diatomic Gases,” Chester W. Smith, Journal of 

Aeronautical Science, June 1946 

18) Advisory Circular 25-20, “Pressurization, Ventilation, and Oxygen Systems Assessment 

for Subsonic Flight Including High Altitude Operation”, dated 9/10/96 

19) Advisory Circular 20-128A, “Design Considerations for Minimized Hazards Caused by 

Uncontained Turbine Engine and Auxiliary Power Unit Rotor Failure, dated 3/25/1997