BEFORE THE 

FEDERAL AVIATION ADMINISTRATION 

WASHINGTON D.C. 

 Docket FAA-2011-___________ 

PETITION OF DELTA AIR LINES, INC. 

FOR AN EXEMPTION 

June 6, 2011 

Delta Air Lines, Incorporated, operating certificate DALA026A, hereby petitions the Federal 

Aviation Administration (FAA), pursuant to 14 C.F.R. Part 11 for partial relief from Federal 

Aviation Regulation (FAR) §121.333 (e)(2), provided certain conditions and limitations are met. 

All references to altitude will be in Mean Sea Level (MSL) unless specifically stated otherwise. 

Use of the name Delta or Delta Air Lines is to be considered the same as Delta Air Lines, 

Incorporated. 

Sections of the FARs Affected: 

Section §121.333(e)(2), Supplemental oxygen for emergency descent and for first aid; turbine 

engine powered airplanes with pressurized cabins, states in pertinent part: 

(e) Passenger cabin occupants. When the airplane is operating at flight altitudes above 

10,000 feet, the following supply of oxygen shall be provided for the use of passenger cabin 

occupants: 

(2) When an airplane is operated at flight altitudes up to and including flight level 250 

and cannot descend safely to a flight altitude of 14,000 feet within four minutes, or when 

an airplane is operated at flight altitudes above flight level 250, oxygen shall be available 

at the rate prescribed by this part for not less than 10 percent of the passenger cabin 

occupants for the entire flight after cabin depressurization, at cabin pressure altitudes 

above 10,000 feet up to and including 14,000 feet and, as applicable, to allow 

compliance with §121.329(c)(2) and (3), except that there shall be not less than a 10 

minute supply for the passenger cabin occupants.

Requested Relief:

Delta Air Lines requests exemption to allow an airplane following a cabin depressurization event 

to initially descend to 14,000 feet and subsequently descend to 10,000 feet no later than 30 

minutes after the initial depressurization event, without carrying the additional supplemental 

oxygen required by Section §121.333(e)(2). 

Petition of 

DELTA AIR LINES, INC. 

OPERATING CERTIFICATE DALA026A

For exemption of certain requirements 

of 14 C.F.R. §121.333(e)(2) 
Petition for Exemption - (FAR) §121.333 (e)(2) 

Delta Air Lines, Inc. 

June 6, 2011 

Page 2 

This exemption request adheres to the premise of §121.329(c)(1) which allows turbine powered 

airplanes to operate at cabin pressure altitudes above 10,000 feet up to and including 14,000 

feet for 30 minutes before requiring additional supplemental oxygen for 10 percent of the 

passengers. §121.329(c)(1) states the following in pertinent part: 

§121.329 - Supplemental oxygen for sustenance: Turbine engine powered airplanes. 

(c) Passengers. Each certificate holder shall provide a supply of oxygen for passengers in 

accordance with the following: 

(1) For flights at cabin pressure altitudes above 10,000 feet, up to and including 14,000 

feet, enough oxygen for that part of the flight at those altitudes that is of more than 30 

minutes duration, for 10 percent of the passengers. 

Background: 

The last amendment to the passenger supplemental oxygen carrying requirements was in 1958. 

The amendment established a requirement to supply supplemental oxygen for 10 percent of the 

passengers for the entire time the aircraft cabin altitude is above 10,000 feet MSL up to and 

including 14,000 feet MSL after a depressurization event. This part of the rule applied to aircraft 

certified to operate to 25,000 feet MSL that could not descend to 14,000 feet MSL within four 

minutes or any aircraft operating above 25,000 feet MSL. For the maximum size of aircraft 

operating at that time the rule would require the carriage of supplemental oxygen for 

approximately 15 passengers if the aircraft could not descend to 10,000 feet MSL after a 

depressurization event and the normal passenger oxygen system supply was not enough for the 

time above 10,000 feet MSL. This would generally require the carriage of 15 portable oxygen 

bottles. 

Manufacturers design most modern aircraft to descend from the maximum certified altitude to 

14,000 feet MSL within four minutes with enough supplemental oxygen to reach 10,000 feet 

within the normal passenger oxygen system supply. Passenger oxygen systems are certified to 

a minimum of 12 minutes for aircraft operated by Delta Air Lines. In many areas of our 

operation Delta has specifically designed depressurization routes that allow the aircraft to 

descend to 10,000 feet MSL within the 12 minute passenger oxygen supply to comply with 

§121.333(e)(2). Once at or below 10,000 feet MSL oxygen is no longer required for compliance 

with §121.333(e)(2). Depending on the airplane location and surrounding terrain, these routes 

may require the aircraft to be operated below grid MORAs (Minimum Off Route Altitudes) on 

defined routes. In layman’s terms, this procedure often requires the pilots to navigate around 

areas of high terrain instead of flying above the terrain. 

Delta operates to over seventy countries within six continents. We consistently use our Safety 

Management System (SMS) to identify hazards and reduce risks to our operation. Due to our 

global network, our flight crews could operate in many theaters spanning six continents in a 

given month. This makes Delta unique compared to the majority of other air carriers who do 

not need to prepare their flight crews for such a diverse operation. Using our internal risk 

assessments, SMS, and pilot training programs we develop procedures and curricula to prepare 

our crews, which will be described later in this petition. One of these procedures and challenges 

is operating over critical terrain. Ninety-five percent of the routes operated by Delta Air Lines 

allow an immediate descent to 10,000 feet MSL after a depressurization. However, 

approximately five percent of the operation is over critical terrain airspace where the grid 

MORAs are above 10,000 feet and immediate descent to 10,000 feet is not possible without 

being established on a published airway or a Delta-engineered route. These areas are primarily 
Petition for Exemption - (FAR) §121.333 (e)(2) 

Delta Air Lines, Inc. 

June 6, 2011 

Page 3 

in Western Canada, Central America, South America, the Middle East, the Himalayas and 

Greenland. 

A depressurization event is a higher risk situation. The flight crew must don oxygen masks, deal 

with the situation that caused the depressurization, perform an emergency descent to a safe 

altitude and, if over critical terrain, transition to a critical terrain route in order to avoid the 

terrain while descending to 10,000 feet MSL within the time limitation of the passenger 

supplemental system. In certain parts of our network, such as South America, pilots face the 

likelihood of executing these critical terrain procedures at night or in the weather, greatly adding 

to the complexity of the maneuver and exacerbating the challenge of maintaining situational 

awareness. 

In order to comply with §121.333(e)(2), Delta employs three methods: 

1. Avoid the critical terrain areas where descent to 10,000 MSL is not possible within the 

supply of the onboard oxygen system. This option creates less efficient routes. 

2. Operate over the terrain where immediate descent to 10,000 feel MSL is not possible but 

provide the crews with specific critical terrain diversion routes that allow initial descent to 

14,000 feet then further descent to 10,000 feet MSL within the time of standard oxygen 

supply (normally 12 minutes). 

3. Certain fleets have been configured with additional supplemental oxygen to allow 

additional time to remain at 14,000 feet MSL. All of the B-777 aircraft operated by Delta 

carry 32 bottles of supplemental oxygen. For certain B-767-300 aircraft, Delta has the 

capability to place a minimum of 24 supplemental bottles in specially configured 

overhead bins. In this case the bottles take up overhead passenger carry-on storage 

capacity by at least six bins. The cost to carry the extra oxygen bottles in direct fuel cost 

for the B-777 is $339,212.00 annually based on fuel price as of March 23, 2011. This is 

fuel that is burned in order to carry the extra weight. In addition to the increased cost 

and fuel burn, the carriage of the additional oxygen bottles increases Delta’s carbon 

footprint and is not environmentally friendly. 

Through our Safety Management System (SMS), Delta has previously identified operations over 

high terrain as an increased risk operation. Currently there are several risk mitigation elements 

in place. These include: 

• Theater Qualification for the pilots 

• Pilot qualification training and continuing qualification training with respect to critical 

terrain procedures 

• Engineered terrain avoidance routes 

• Flight planning system identifying to the flight crews when a route requires special 

depressurization routes 

• Aircraft theater equipment restrictions requiring certain operational equipment above 

regulatory requirements, e.g., not always allowing Minimum Equipment List (MEL) relief 

for enhanced ground proximity warning systems depending on the planned route 

While these mitigations make operations in areas of high terrain acceptable, there is still the 

latent condition of controlled flight into terrain (CFIT) inherent anytime the aircraft is required to 

operate below a grid MORA. Raising the initial descent to 14,000 feet MSL for 30 minutes 

removes the vast majority of CFIT risk associated with critical terrain areas. Attached to this 

request are 8000 foot MSL and 12,000 foot MSL maps for a parts of South America, Middle East 

and Greenland, illustrating the reduction of the terrain risk by initially descending to 14,000 feet 

MSL versus the current requirement to descend to 10,000 feet MSL. See Appendix 1. 
Petition for Exemption - (FAR) §121.333 (e)(2) 

Delta Air Lines, Inc. 

June 6, 2011 

Page 4 

Justification for exemption: 

Delta’s goal of this exemption request is to reduce CFIT risk by reducing the complexity of the 

operation and improving the situational awareness of our flight crews in the first few minutes 

after a depressurization event. A typical CFIT accident has a root cause of the pilot losing 

situational awareness generally due to a flight deck distraction. Typical accident scenarios have 

an error chain that compounds throughout the event. By its very nature, a depressurization 

event is a higher risk event posing a significant distraction that the flight crew must deal with. 

The requirement to descend into areas of high terrain adds another level of complexity to the 

operation. Other than the issue of the rule requiring a supply of oxygen be available to 10 

percent of the passengers while operating above 10,000 feet up to and including 14,000 feet, it 

is self-evident that flying over high terrain poses a lower degree of CFIT risk than operating 

around the terrain. Our petition demonstrates that we can remove a significant amount of CFIT 

risk associated with a depressurization event and provide at least an equivalent level of safety 

with respect to the physiological aspect of 121.333(e)(2). At the same time, the Delta proposal 

will remove a hazardous materials risk associated with carrying large quantities of oxygen 

aboard the aircraft. 

Delta’s Flight Safety and Quality Assurance departments have conducted a 10-year review of 

NTSB files for United States air carriers and found 8 reports where a rapid decompression was 

part of the incident or accident. We limited our review to United States air carriers because all 

aircraft are under one set of maintenance rules and are established in the required aging aircraft 

programs as appropriate. Each of these events is cited below. Of the 8 events, 2 occurred 

during a ground operation where a door was opened while the aircraft had some level of 

pressurization. The other 6 depressurization events occurred within the first 25 minutes of flight 

based on the narrative of the reports. 

• MIA01FA029 , (Miami, FL – 2000) – After takeoff aircraft did not properly pressurize. 

Ground accident due to aircraft remaining pressurized on the ground after landing and a 

Flight Attendant being thrown from aircraft while opening a door. 

• DEN05LA077, (Denver, CO – 2005) – Shortly after takeoff part of the nose landing gear 

punctured the forward pressure bulkhead.(below 10,000 feet MSL). Aircraft returned for 

landing. 

• DCA05MA071, (Chicago, IL – 2005) – Aircraft inadvertently pressurized on the ground. Flight 

Attendant thrown from the aircraft while opening the door 

• SEA06LA033, (Seattle, WA – 2005) - During the climb out, at approximately 26,000 feet cargo 

door skin developed a 12 inch by 6 inch hole. Flight returned for landing. 

• NYC07LA121, (Syracuse, NY – 2007) - After departure, the airplane was climbing through 

approximately 20,000 feet mean sea level (MSL) the aircraft developed a 12-inch by 5-inch 

fuselage skin tear in front of the cargo door. Flight diverted to a nearby suitable airport. 

• DCA09FA065, (Charleston, WV – 2009) – Approximately 25 minutes after takeoff aircraft 

developed a 18-inch by 12-inch flap in the skin. Flight diverted to a nearby suitable airport. 

• DCA11FA004, (Miami, FL – 2010) - Approximately 25 minutes after takeoff at 31,000 feet MSL 

aircraft developed a hole of about 1 foot by 2 feet. Flight returned for landing. 

• DCA11MA039 , (DCA, DC – 2011) – Approximately 20 minutes after takeoff at approximately 

34,000 feet MSL aircraft developed a 5 foot by 1 foot hole over the passenger cabin aft of the 

wing. Flight diverted to a nearby suitable airport 

In the past 10 years Delta Air Lines has flown approximately 26,284,023 flight hours and 

11,313,568 flights (data combined with previous Northwest Airlines). Considering Delta and 

Northwest each had one event, we calculate the actual rate of occurrence at 7.609 x 10-8 per 
Petition for Exemption - (FAR) §121.333 (e)(2) 

Delta Air Lines, Inc. 

June 6, 2011 

Page 5 

flight hour with a 95% confidence interval of 1.0546 x 10-7. Our calculations appear to be 

consistent with a recent publication by the FAA noted below. During our research Delta did not 

find any events within the past 10 years where a Delta or a Northwest aircraft experienced a 

rapid depressurization event over critical terrain where an immediate descent to 10,000 feet 

was not possible. Both events associated with Delta and Northwest occurred within the first 20 

minutes of departure. It is our contention that relief from §121.333(e)(2) as requested would 

be inconsequential based on event probability alone. 

In a recent final rule (Docket No. 2011-0186) the FAA stated the following with respect to use of 

the oxygen system other than a malfunction of the pressurization system: 

“The FAA has conducted a risk analysis to assess the safety implications of temporarily 

not having supplemental oxygen available inside lavatories. To support the risk 

assessment, earlier studies involving passengers' use of oxygen were reviewed. For a 

different rulemaking, the FAA tasked the Aviation Rulemaking Advisory Committee 

(ARAC) to make recommendations for safety standards when airplanes are operating at 

high altitudes. As part of its effort, the ARAC did a comprehensive assessment of the 

frequency and nature of the need for supplemental oxygen systems in service. The 

ARAC identified 2,800 instances over a 40-year period and categorized them by cause, 

severity, and consequence. The majority of these instances were caused by 

malfunctions of the cabin pressurization system. However, in none of those 2,800 

instances was there a loss of life due to lack of oxygen. The ARAC used these 

data in making recommendations to the FAA on future rulemaking. 

The FAA has reviewed the service history since the ARAC recommendations were made 

and found that the types and frequencies of incidents, as well as their causes, are 

consistent with the historical record. The relative risks and service history have not 

changed in any significant way since the ARAC recommendations were issued. With 

respect to this SFAR, the only affected areas of the airplane are the lavatories, as 

opposed to the earlier assessments, which applied to the entire airplane. The lavatories 

are sporadically occupied during flight, and by a small number of passengers at any 

given time. This limits the potential impact on safety. 

The ARAC found that the frequency of occurrences necessitating the use of 

oxygen was around 10-

\8\/flight-hour for causes other than a malfunction of 

the pressurization system (these tend to be slower losses of pressure, or are 

identified at lower altitudes, and therefore are not as critical for this action). The 

probability that a lavatory will be occupied at any given moment is not known. It is not 

100% and it is not 0%. If, for the purposes of this assessment, we assume the 

probability is 50%, then the probability of a person in a lavatory needing oxygen is ~5 

x 10-9/flight-hour.” 

(Emphasis added) 

When we consider that 95% of our operation is over terrain that allows an immediate descent to 

10,000 feet MSL the potential impact to safety is at least comparable to the FAA’s analysis 

within Docket No. 2011-0186

Support for Requested Action and Equivalent Level of Safety 

In order to demonstrate no adverse effect to public safety, Delta conferred with Dr. Allen J. 

Parmet, an aerospace medical doctor, to establish the physiological aspects of this proposal for 
Petition for Exemption - (FAR) §121.333 (e)(2) 

Delta Air Lines, Inc. 

June 6, 2011 

Page 6 

exemption. Specifically we requested that Dr. Parmet provide an analysis so Delta could 

compare the physiological aspects between §121.329(c)(1), Supplemental oxygen for 

sustenance: Turbine engine powered airplanes and this proposal to be exempt from supplying 

the additional oxygen required by §121.333(e)(2). 

See Appendix 2. 

Additionally, we wanted to assess whether or not this proposal would deliver an equivalent level 

of oxygen to passenger aircraft operated under §121.329(c)(1) if not required to operate under 

§121.333(e)(2). Dr. Allen J. Parmet provided a position paper to Delta Air Lines on 3/24/2011. 

Following receipt of Dr. Parmet’s position paper Delta requested additional data and analysis for 

the following two scenarios: 1) Slow decompression at 42,000 feet with descent to 14,000 feet, 

and 2) Rapid decompression at 42,000 feet with descent to 14,000 feet. We wanted to assure 

that individuals breathing supplemental oxygen will have an oxygen level comparable to an 

individual at 14,000 feet without supplemental oxygen. We requested that Dr. Parmet provide 

the oxygen values for a slow and a rapid decompression assuming an initial oxygen flow rate of 

3.6 L/min. for four minutes and a lower rate of 0.8 L/min. for the duration of the oxygen 

generator time. The slow decompression chart represents a conservative view of either a 

smaller aircraft skin failure or a loss of pressurization system where the cabin reaches 25,000 

feet before the passenger begins the use oxygen. The systems are designed to automatically 

deploy the oxygen masks if the cabin altitude exceeds 14,000 feet. For the rapid decompression 

an assumption was made that the cabin altitude reached 40,000 feet before the passengers 

began to use the oxygen. 

Decompression Incident Scenarios 

Scenario 1: Slow decompression at 42,000 feet with descent to 14,000 feet 

Elapsed 

Time In 

Minutes 

Cabin 

Altitude 

(Aircraft 

Altitude)

Cabin 

Barometric 

Pressure 

(PB) 

Cabin Partial 

Pressure of 

Oxygen (PO2) 

Arterial 

Oxygen 

Level 

(PaO2) 

Equivalent 

Altitude 

Time of Useful 

Consciousness 

0 8,000’ 

42,000 

565 mmHg 118 mmHg 69 mmHg N/A Indefinite 

1 15,000’ 

32,000’ 

429 mmHg 90 mmHg 45 mmHg N/A Indefinite 

2 25,000’ 

25,000’ 

282 mmHg 59 mmHg 30 mmHg N/A 3-5 minutes 

2 25,000’ 

25,000’ 

282 mmHg Oxygen 

Generator Used 

@ 3 LPM 

135 mmHg 

87 mmHg ~3500’ Indefinite 

4 14,000’ 

14,000’ 

446 mmHg Oxygen 

Generator Used 

at 0.8 LPM 110 

mmHg 

61 mmHg ~10,000’ Indefinite 

16 14,000’ 

14,000’ 

446 mmHg Oxygen 

Generator 

Expired 

94 mmHg 

48 mmHg N/A Indefinite 

Note: Equivalent altitudes derived from: Fundamentals of Aerospace Medicine, Fourth Edition 
Petition for Exemption - (FAR) §121.333 (e)(2) 

Delta Air Lines, Inc. 

June 6, 2011 

Page 7 

Scenario 2: Rapid decompression at 42,000 feet with descent to 14,000 feet 

Note: Equivalent altitudes derived from: Fundamentals of Aerospace Medicine, Fourth Edition 

Key points of Dr. Parmet’s position paper and decompression analysis: 

• At a cabin altitude of 25,000 feet MSL at a 3.6 L/min flow rate the passenger is at an 

altitude equivalent of approximately 3500 feet MSL. At a cabin altitude of 14,000 feet 

MSL at a 0.8 L/min flow rate the passenger is at an altitude equivalent of approximately 

10,000 feet MSL. 

• At a cabin altitude of 40,000 feet MSL at a 3.6 L/min flow rate the passenger is at an 

altitude equivalent of approximately 3000 feet MSL. The reason for the lower equivalent 

altitude vs 25,000 feet is due to the higher barometric pressure at the lower altitude 

which creates more mixing of the 21% oxygen ambient air with the oxygen being 

delivered. 

• The passenger in both cases will be provided with an initial oxygen equivalency lower 

than 8000 feet and by the time the oxygen generator expires (approximately 12 

minutes) will be no higher than 10,000 feet. From this point the passenger will be 

breathing ambient air of 14,000 feet for approximately 18 minutes when our procedures 

will allow the aircraft to have descended to at least 10,000 feet MSL. 

• By 15,000 feet the use of supplemental oxygen is not necessary for individuals with 

normal pulmonary function. 

• For individuals with compromised pulmonary function the aircraft oxygen system will 

initially supply the necessary oxygen equivalent to the passenger carried oxygen systems 

Elapsed 

Time In 

Minutes 

Cabin 

Altitude 

(Aircraft 

Altitude)

Cabin 

Barometric 

Pressure 

(PB) 

Cabin Partial 

Pressure of 

Oxygen (PO2) 

Arterial 

Oxygen 

Level 

(PaO2) 

Equivalent 

Altitude 

Time of Useful 

Consciousness 

0 8,000’ 

42,000 

565 mmHg 118 mmHg 69 mmHg N/A Indefinite 

0.1 40,000’ 

42,000 

141 mmHg 32 mmHg 10 mmHg N/A 10 seconds 

0.2 40,000’ 

40,000’ 

141 mmHg Oxygen 

Generator Used 

@ 3 LPM 

141 mmHg 

90 mmHg ~3,000’ Indefinite 

2 25,000’ 

25,000’ 

282 mmHg Oxygen 

Generator Used 

@ 3 LPM 

135 mmHg 

87 mmHg ~3500’ Indefinite 

4 14,000’ 

14,000’ 

446 mmHg Oxygen 

Generator Used 

at 0.8 LPM 110 

mmHg 

61 mmHg ~10,000’ Indefinite 

16 14,000’ 

14,000’ 

446 mmHg Oxygen 

Generator 

Expired 

94 mmHg 

48 mmHg N/A Indefinite 
Petition for Exemption - (FAR) §121.333 (e)(2) 

Delta Air Lines, Inc. 

June 6, 2011 

Page 8 

allowed on the aircraft. When the system transitions to the lower flow the passenger 

should be able to resume their own system use or be aided by a first aid bottle. 

Delta Air Lines Analysis and Public Interest: 

FAR §121.329(a)(1) allows indefinite flight at a cabin altitude of 10,000 feet MSL then allows 30 

minutes of flight up to and including a cabin altitude of 14,000 without supplying any additional 

passenger oxygen. With the requirement of §121.333(e)(2), which references compliance to 

§121.329(c)(2) and (3), 100 percent of the passengers will have access to at least a 12 minute 

oxygen supply for all Delta aircraft. During this time the passenger will be supplied with an 

oxygen equivalent of 10,000 feet MSL or lower. Delta is requesting to remain at 14,000 feet 

MSL for a maximum of an additional 18 minutes after the depletion of the oxygen generators 

before completing a descent to or below 10,000 feet MSL. Therefore, we believe that our 

proposal is still more conservative than an operation that is only required to comply with 

§121.329 which allows 30 minutes at 14,000 feet MSL with no supplemental oxygen. 

While we would concur that other regulatory statutes do not directly effect the determination for 

granting an exemption, we believe it is important for the FAA to recognize that several foreign 

regulators allow flight up to 30 minutes at cabin altitudes above 10,000 feet MSL before requiring 

additional passenger oxygen. EASA (European Aviation Safety Agency) allows operations above 

10,000 feet MSL up to and including 14,000 feet MSL for 30 minutes before requiring additional 

oxygen for the passengers. See Appendix 3. Many of the air carriers certified by EASA are 

also certified by the Federal Aviation Administration under 14 CFR §129. In cases where Delta 

has to route aircraft around the areas of terrain above 8,000 feet MSL in order to comply with 

§121.333, these other carriers are operating on more direct and efficient routes. For the remote 

chance of a Delta aircraft having a decompression over a critical terrain area, the pilots would be 

restricted on routing options compared to a carrier not restricted by 121.333(e)(2). This creates 

the potential of greater flight time to landing after a decompression. 

Delta completed a review to modify and equip aircraft that operate in areas of critical terrain 

with additional supplemental oxygen to allow operations on the same routes as our competitors. 

To equip all aircraft that operate on routes over critical terrain would require the purchase of 

over 9700 supplemental oxygen bottles. Using a cost estimate of $100.00 each results in a cost 

just under one million dollars. The annual fuel expense to carry the extra bottles on fleets that 

operate in areas of critical terrain would exceed 6 million dollars per year on a fleet wide basis. 

The engineering, onboard storage, installation and maintenance costs would far exceed this cost 

and put Delta at an economic disadvantage to our competitors who are not required to comply 

with §121.333(e)(2). Additionally, if Delta proceeded with the equipage option, it would create 

increased greenhouse gas effects making this option economically and environmentally 

prohibitive. If the exemption is denied, there is a high probability that the cost to operate would 

be passed on to the traveling public. Consequently, after carefully considering the fact that the 

additional oxygen required by §121.333(e)(2) has never been used to serve a passenger during 

operations at Delta, combined with the environmental and economic impact associated with 

equipping the fleet, equipping with additional supplemental oxygen is not in the public’s best 

interest. 

Delta has also identified a hazardous materials risk associated with carrying large quantities of 

oxygen. In the event several of these bottles were turned on in a confined space with other 

flammable materials the area could ignite creating a severe fire and possible explosion. 

Considering Delta has never experienced a flight where these bottles were actually required due to 

a loss of pressurization along with the very low probability of a depressurization event over a 
Petition for Exemption - (FAR) §121.333 (e)(2) 

Delta Air Lines, Inc. 

June 6, 2011 

Page 9 

terrain critical area, Delta contends it is in the public interest to grant this exemption so we may 

remove this hazard from the aircraft currently equipped. Equipping other aircraft would simply 

provide more opportunities for the event described. While an argument could be made to secure 

the bottles in a locked area, this would seem to defeat the purpose of “availability” as well as 

create additional expense to configure the aircraft. 

Proposed Conditions and Limitations for Grant of Requested Exemption 

Delta proposes the following as conditions for grant of the exemption: 

1. Delta will maintain a database/history for each depressurization event where oxygen masks 

deployed. The data required will at a minimum contain: 

a. Flight number and date 

b. City pair 

c. Departure time 

d. Time after takeoff of occurrence 

e. Area of decompression (critical terrain) 

f. Aircraft altitude of event 

g. Maximum cabin altitude experienced 

h. Cause of the event 

i. Narrative summary 

2. For this exemption to remain in effect, Delta must maintain or exceed its current record 

of 7.6 x 10-8 events per flight hour (within 3 standard deviations), for events that exceed 

a cabin altitude of 25,000 feet MSL over a 10 rolling year period. 

3. At least once each quarter Delta will review items 1 and 2 with the Principal Operations 

Inspector to ensure compliance. 

Request for Relief is Non Precedent Setting 

The Federal Aviation Administration has previously granted deviation from the requirements of 

§121.333(e)(2) utilizing 14 CFR §119.55. Delta was granted Operations Specifications A525, 

Oxygen Supply: Passenger Cabin Occupants. See appendix 4. In this deviation the FAA 

granted relief from §121.333(e)(2) for up to 20 minutes for international supplemental 

operations associated with Iraqi Freedom. 

Conclusion 

The purpose of a safety management system is to continuously identify hazards and reduce risks to 

the operation and traveling public. The hazard of controlled flight into terrain will be reduced by 

granting Delta exemption from §121.333(e)(2). 

In consideration of this petition based on the information contained above, Delta maintains that 

it is prudent for the FAA to grant Delta Air Lines an exemption to allow aircraft after a 

depressurization event to initially descend to 14,000 MSL feet then to descend to at least 10,000 

feet no later than 30 minutes after the initial depressurization event without carrying the 

additional oxygen required by §121.333(e)(2). The Delta proposal reduces the risk of controlled 

flight into terrain, provides more direct flight paths to land after a depressurization event and 

removes a hazardous materials risk. Delta demonstrates an equivalency based on a 

physiological analysis and comparison to other Federal Aviation Rules. The public interest is met 
Petition for Exemption - (FAR) §121.333 (e)(2) 

Delta Air Lines, Inc. 

June 6, 2011 

Page 10 

by the elements stated above plus an economic and environmental element that demonstrates 

how equipage will not justify the cost and pose an additional hazard. 

Summary 

Delta Air Lines requests exemption to allow the aircraft after a depressurization event to initially 

descend to 14,000 feet then to descend to at least 10,000 feet no later then 30 minutes after 

the initial depressurization event without carrying the additional oxygen required by 

§121.333(e)(2) provided certain conditions and limitations are met. Granting this exemption 

will reduce the controlled flight into terrain (CFIT) risk associated with a decompression event. 

Please contact Charles M. Schramek, General Manager Quality Assurance and Compliance, at 

(404) 715-1112 or e-mail at chuck.schramek@delta.com, if you have and questions or need 

additional information. 

Sincerely, 

Stephen M. Dickson 

Senior Vice President Flight Operations 

Delta Air Lines, Inc. 

cc: Steve Gorman, Chief Operating Officer – Delta Air Lines 

 Ken Hylander, Senior Vice President Corporate Safety, Security, and Compliance – Delta Air Lines 

 Lisa Brockenbrough, Director, Flight Safety – Delta Air Lines 

 Charles M. Schramek, General Manager Quality Assurance and Compliance – Delta Air Lines 

 Thomas Stachiw, Office Manager Delta Certificate Office – FAA 

 David Gerken, Acting Office Manager Delta Certificate Management Unit– FAA 

 James T. Giles, Jr, Principal Operations Inspector Delta Certificate Management Unit – FAA 
Petition for Exemption - (FAR) §121.333 (e)(2) 

Delta Air Lines, Inc. 

June 6, 2011 

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Appendix 1 
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Appendix 2 

DEPRESSURIZATION EFFECTS ON COMMERCIAL AIRCRAFT 

By: Dr. Allen J. Parmet

PART I – ALTITUDE PHYSIOLOGY

The basic problem of altitude change involves the decrease in total barometric pressure as well as the partial 

pressure of oxygen. At sea level, barometric pressure is 14.7 PSI/760 mmHg/29.92 inHg. Note that in this 

paper, we will only use the metric measurements of millimeters of mercury (mmHg) as the standard used 

within the scientific community. The table will contain an equivalent pounds per square inch (PSI) notation. 

Humans must have sufficient barometric pressure to keep their blood from boiling. The atmospheric pressure 

drops to this level of 47 mmHg (0.9 PSI) at an altitude of 63,000 feet. At this altitude, the boiling point of water 

is the same as normal human body temperature or 37 ̊C./98.6 ̊F. This represents an absolute altitude 

limitation without pressurization. 

Humans also require a sufficient amount of oxygen so that their body, and in particular the brain, functions. 

The human brain only operates aerobically; that is, it requires oxygen for its metabolism. Other organs of the 

body, such as muscles, skin and bone, can function anaerobically for prolonged periods of time although the 

metabolism is far less efficient and result in a buildup of lactic acid. The minimum level of oxygen reaching the 

alveoli of the lungs for normal brain function is a pressure of 45 mmHg. 

Oxygen is present at 21% of the atmosphere at all altitudes. Thus, when the barometric pressure drops, the 

partial pressure of oxygen also drops while the composition remains constant at 21%. This permits an aircraft 

at altitude to compress the ambient air to a pressure sufficient for normal human function. Current commercial 

aircraft are limited to a cabin altitude maximally of 8,000 feet or a barometric pressure of 565 mmHg/10.9 PSI. 

The partial pressure of oxygen drops from 160 mmHg at sea level to 118 mmHg at 8,000 feet. The resulting 

oxygen delivered to the lung, known as the PaO2, is 69 mmHg. The tabular representation of this is in the 

attached table. 

Up to an altitude of 15,000 feet, there is sufficient oxygen in the ambient air for normal human operation due to 

the ability of the body to compensate. Compensation is a complex function and manifested by several 

physiologic changes. First, the rate of respiration, or number of breaths per minute, increases as to the depth 

of respiration. The volume is significantly increased as well. Our normal breath will take in only about 500 

milliliters of air, but under these circumstances a respiration could be increased to 800 or even 1,000 milliliters 

per breath and respiratory rate will climb from 14 per minute to 20-24. This increased rate of respiration also 

results in increased exhalation of the waste product carbon dioxide (CO2). CO2 is a weak acid and removal of 

this acid from the blood stream alters the blood pH from a normal 7.40 to as high as 7.44. While this seems 

slight, the change in acidity of the blood alters the hemoglobin within red blood cells and increases their ability 

to capture oxygen while passing through the lungs. Thus, a human has the reserve capacity to become more 

efficient and collect a higher percentage of oxygen from inspired air at high altitude. 

If high altitude hypoxia is maintained for a longer period of time than just a few hours, the effect of the lower 

oxygen level on the kidneys causes the kidneys to secrete a hormone known as erythropoietin (EPO). The 

EPO hormone will cause bone marrow to produce more red blood cells, thus providing increased carrying 

capacity. Within 3-4 days, the blood carrying capacity can be increased as much as 5% and over several 

weeks, up to 10%. Individuals who live at high altitudes will typically have blood counts 10% higher than 

people living at sea level. This latter is termed a chronic adaptation. A mild effect is seen in all aircrew that 

spend many hours per month at altitude and periodically experience hypoxia. 
Petition for Exemption - (FAR) §121.333 (e)(2) 

Delta Air Lines, Inc. 

June 6, 2011 

Page 18 

Under normal operating conditions, an aircraft cabin at 8,000 feet results in no physiologic changes in a 

normal individual and indeed, at 12,000 feet can be tolerated for an indefinite period of time in most 

individuals. 

The rare person, about 1 in 20, when exposed to an altitude of 12,000 feet or more for greater than 12 hours 

can begin to develop illnesses called high altitude pulmonary edema (HAPE) and high altitude cerebral edema 

(HACE). These are treated by descent. The nature of physiologic adaptation is easily demonstrated by 

mountain climbers who are able to climb Mount Everest (29,029 feet) without supplemental oxygen by using 

the physiologic adaptation process over a period of weeks. Even so, at that extreme altitude, they do so under 

a condition of marked physiologic compromise. 

PART II – RESPIRATORY COMPROMISE IN PASSENGERS

The American Thoracic Society describes characteristics of individuals who have developed pulmonary and 

respiratory compromise as Respiratory Class I, II, III and IV based upon certain standards, with Class I being 

the least serious and Class IV being the worst. Any disease such as emphysema, fibrosis or trauma may 

destroy so much lung function that an individual is no longer considered to be normal based upon the objective 

measurements. 

A Class I individual, however, is able to function normally and perform all their activities although at a reduced 

level. Class II individuals will become short of breath with minimal physical exertion. They generally become 

significantly short of breath climbing a flight of stairs or walking 50 feet. Class III individuals will be short of 

breath even at rest and may require supplemental oxygen for normal activity. Class IV individuals are severely 

compromised and require supplemental oxygen to maintain life. 

Supplemental oxygen consists of increasing the percentage of oxygen in the inspired air. The percentage of 

oxygen in the atmosphere is as noted above, 21% at all altitudes. The term for fraction of inspired oxygen 

percentage is FIO2. Most supplemental oxygen is delivered by a device known as a nasal cannula, which is a 

tube ending in two short prongs with one going into each nostril. A nasal cannula can deliver supplemental 

oxygen up to about 36%, which requires a flow of approximately 8.0 L/min. Even at this level, a nasal cannula 

is quite compromised and very uncomfortable to wear. It is rarely used at flows above 4.0 L/min, which can 

deliver an FIO2 of 28%. When the FIO2 required is between 28 and 40%, then a mask is used. These 

breathing masks will have apertures in them that permit mixing of ambient air. To achieve an FIO2 of greater 

than 40%, a close-fitting, sealed mask, typically termed “aviator’s mask”, must be used. However, an FIO2 of 

greater than 40% will create the risk of oxygen toxicity. The results are an injury to the lungs caused simply by 

the high levels of oxygen and free radical formation. Therefore, individuals cannot generally be maintained on 

a high FIO2 indefinitely and such levels are in general only used for hospitalized patients. 

The issue of high FIO2 in aircrew would be true except for the fact that the barometric pressure drops, resulting 

in an absolute level of oxygen, that is the partial pressure, is the equivalent of sea level pressure and therefore 

toxicity is not an issue in aviation, even when breathing 100%. 

PART III – DECOMPRESSION EVENTS

If a commercial aircraft is operating at an altitude between 33,000 feet and 42,000 feet with a cabin pressure 

of 8,000 feet above sea level, the passengers will not experience any physiologic compromise. If loss of cabin 

pressurization occurs, however, the barometric pressure drops to ambient and the partial pressure of oxygen 

drops to the point that the ability of an individual to function, known as the Time of Useful Consciousness or 

Effective Performance Time, becomes only a few seconds. Therefore, supplemental oxygen is imperative. 

Aircrew are equipped with quick-donned aviators masks capable of delivering 100% oxygen. At an altitude of 

33,000 feet, 100% oxygen becomes physiologically equivalent to breathing normal air at sea level. This is to 

say that the barometric pressure at 33,000 feet is effectively the same as the partial pressure of oxygen at sea 

level. Above this altitude, less and less oxygen becomes available to the brain even though supplemental 
Petition for Exemption - (FAR) §121.333 (e)(2) 

Delta Air Lines, Inc. 

June 6, 2011 

Page 19 

oxygen up to 100% is used. Therefore, descent to a safer altitude is critical. However, it is most critical that 

the aircraft be flown in a safe manner and not strike terrain. Remaining at a safe altitude is more imperative 

than supplying oxygen to passengers. 

Supplemental oxygen is available to passengers through two methods. Most common is the chemical oxygen 

generator. This canister is installed in the overhead compartment in virtually all commercial aircraft. These 

canisters, such as those manufactured by AVOX Systems or older systems by Puritan Bennett, contain a 

super-oxide chemical. An igniter pin triggers a reaction and the chemical combusts, burning like a solid rocket 

motor. However, the combustion products are typically salts (NaCl or KCl) and oxygen. These canisters can 

produce the equivalent of 7.0 L/min of oxygen flow for the first 3-4 minutes and then an additional 3 L/min of 

oxygen flow for 12-15 minutes (Puritan Bennett and some AVOX models). Other models have lower peak 

flows at 3.6 L/min for the first 4-6 minutes and then an additional 0.8 L/min of oxygen flow for 10 minutes 

(Lockheed AVOX). 

This means that at the initial 7.0 L/min flow, the pressure is approximately 180 mmHg and at 3.6 L/min, it is 

92 mmHg. If the initial flow is 3 L/min, then it is approximately 75 mmHg and at 0.8 L/min it is 20 mmHg. This 

pressure represents oxygen added to the ambient air and displaces the ambient air. The mask used to deliver 

this, a small yellow mask typically called a “margarine cup”, when placed on the face will provide a reasonably 

good seal. A flap valve permits mixing of cabin air with the supplemental oxygen if the ambient pressure is 

higher than the mask pressure. 

Thus, at the high flow of 7.0 L/min when the cabin altitude is above 35,000 feet, there will be little or no 

ambient air mixed in, and the user will effectively be on 100% oxygen. The passenger is physiologically at sea 

level. If the flow is 3.6 L/min, with the ambient pressure at about 197 mmHg, the FIO2 is approximately 60%. 

This is equivalent to a real pressure altitude of 8,000 feet. 

At lower altitudes, cabin air will begin to mix and by an altitude of 18,000 feet where the barometric pressure is 

380 mm and at a 3.0 L/min flow will be approximately 65 mmHg. The mixed gas inspired will be approximately 

38% oxygen. If the flow is 0.8 L/min, then the mixed gas will have an FIO2 of approximately 25%. This is 

equivalent to a real pressure altitude of 14,000. 

The use of the emergency mask will be unnecessary below 15,000 feet although passengers may continue to 

use this until the generator is empty. When the flow stops, the flap valve permits cabin air to enter the mask 

without mixing and minimal resistance, so even an unconscious person would not asphyxiate. 

For individuals with compromised pulmonary function, the emergency use of a chemical oxygen generator 

therefore provides a high enough oxygen flow to be equivalent to any supplemental oxygen they could legally 

use to fly as a passenger. However, when a generator drops to the lower flow, hypoxia will ensue and 

eventually with the generator emptying after 15-18 minutes, these individuals will either need to resume using 

their own supplemental oxygen or be augmented by oxygen provided from the emergency supply by the flight 

crew. With supplemental oxygen, these individuals will function nearly normal, but compromise would be 

anticipated. Without supplemental oxygen, a compromised individual would be expected to lose 

consciousness. However, death does not ensue in respiratory compromised individuals except in the most 

fragile of all cases. These individuals may have been taking excessive risk in their choice to travel by 

commercial air rather than air ambulance, and it will be impossible to provide for all individuals under all 

circumstances, in particular a class III respiratory individual who has assured the transporting airline that they 

were class II or less. 
Petition for Exemption - (FAR) §121.333 (e)(2) 

Delta Air Lines, Inc. 

June 6, 2011 

Page 20 

RESPIRATORY FUNCTION AT ALTITUDE

WITH THE ADDITION OF SUPPLEMENTAL OXYGEN AT HIGHER ALTITUDES

Altitude Barometric 

Pressure (PB) 

Partial Pressure of 

Oxygen (PO2) 

Arterial Oxygen 

Level (PaO2) 

Time of Useful 

Consciousness 

Sea Level 

FIO2 21% 

14.7 PSI/ 

760 mmHg 

160 mmHg 103 mmHg Indefinite 

8,000’ 10.9 PSI/ 

565 mmHg 

118 mmHg 69 mmHg Indefinite 

10,000’ 10.1 PSI/ 

522 mmHg 

109 mmHg 61 mmHg Indefinite 

12,000’ 9.3 PSI/ 

483 mmHg 

101 mmHg 54 mmHg Indefinite 

14,000’ 8.6 PSI/ 

446 mmHg 

93 mmHg 48 mmHg Indefinite 

18,000’ FIO2 

21% 

7.35 PSI/ 

380 mmHg 

80 mmHg 38 mmHg 30 minutes 

18,000’ FIO2 

25% 

7.35 PSI/ 

380 mmHg 

95 mmHg 50 mmHg Indefinite 

33,000’ 

FIO2 21% 

3.81 PSI/ 

197 mmHg 

40 mmHg 23 mmHg 45 seconds 

33,000’ 

FIO2 36% “ “ 

71 mmHg 40 mmHg 15 minutes 

33,000’ 

FIO2 60% “ “ 

118 mmHg 69 mmHg Indefinite 

33,000’ 

FIO2 100% “ “ 

197 mmHg 109 mmHg Indefinite 

42,000’ 

FIO2 21% 

2.48 PSI/ 

128 mmHg 

27 mmHg 8 mmHg 10 seconds 

42,000’ 

FIO2 36% “ “ 

46 mmHg 15 mmHg Approximately 

15 seconds 

42,000’ 

FIO2 100% “ “ 

128 mmHg 41 mmHg Indefinite 
Petition for Exemption - (FAR) §121.333 (e)(2) 

Delta Air Lines, Inc. 

June 6, 2011 

Page 21 

Appendix 3 

EASA Rule 
Petition for Exemption - (FAR) §121.333 (e)(2) 

Delta Air Lines, Inc. 

June 6, 2011 

Page 22 

Appendix 4