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Federal Aviation 

Administration 

Memorandum 

Date: March 16,2010 

From: Tina L. Miller 

Program Manager, ACE-117W 

Wichita Aircraft Certification Office 

To: U.S. Dept of Transportation 

Docket Management System 

Prepared by: Tina L. Miller 

Subject: ACTION: Cessna Aircraft Company Request for Exemption from the Requirements 

of 14 CFR Section §25.1447(cXl), 15,000 ft Cabin Pressure Altitude 

Cessna Aircraft Company has submitted, through the Wichita Ahcrait Certification Office, their request for 

exemption to the requirement listed above as pertains to automatic display of oxygen before the cabin 

altitude exceeds 15,000 feet. 

Attached for you action is the original copy of Cessna letter L390-10-0656, dated March 1,2010. We will 

appreciate you keeping this office infonned regarding any actions taken for this request. 

A copy of this transmioal memorandum and Cessna's request is being sent to the Transport Airplane 

Directorate. The Project Officer for the Cessna Model 680 is Rick Morris, ANM-113. 

If you have any questions, please advise. 

Tina L. Miller 

Attachment 

cc: Rick Morris, ANM-113 
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C^ssra 

A T«KU«n Company 

01 March 2010 

IN REPLY, REFER TO: 

L390-10-0656 

Federal Aviation Administration 

Wichita Aircraft Certification Office 

1801 Airport Road 

Wichita, Kansas 67209 

<1 

^ 

J ^ 

ATTENTION: 

SUBJECT: 

Ms. Tina Miller 

Cessna Program Manager 

Model 680, Petition for Exemption firom the Requirements of 14 CFR 

25.H47(c)(l), 15,000 ft Cabin Pressure Altitude 

Dear Ms. Miller: 

Cessna reqiiest relief from the following regulations: 

Section 25.1447(cXl) states; "There must be an oxygen dispensing unit connected to oxygen 

supply terminals immediately available to each occupant, wherever seated, and at least two 

oxygen dispensing units cormected to oxygen terminals in each lavatory. The total number of 

dispensing units and outlets in the cabin roust exceed the number of seats by at least 10 percent. 

The extra units must be as uniformly distributed throughout the cabin as practicable. If 

certification for operation above 30,000 feet is requested, the dispensing imits providing the 

required oxygen flow must be automatically presented to the occupants before the cabin pressure 

altitude exceeds 15,000 feet The crew must be provided with a manual means of making the 

dispensing imits immediately available in the event of a failure of the automatic system." 

An exemption is requested to the portion requiring the dispensing units to be automatically 

presented to the occupants before the cabin pressure altitude exceeds 15,000 feet 

The present aircraft uses Transport Airplane Directorate (TAD) Equivalent Level of Safety 

(ELOS) Memo TC2548WI-T-SG-1 to address suppression of the 10,000 foot cabin pressure 

altitude warning required by 25.841(b)(6) when operating to and firom airports with a field 

elevation fiom 8,000 feet to 14,000 feet 
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L390-10-0656 

Page 2 of3 

To avoid nuisance warnings when operating to and fiom airports with a field elevation from 

8,000 feet to 14,000 feet, an exemption is requested to allow use of a ">14K" switch to shift the 

cabin altitude warning to 15,750 feet. 

The petitioner supports its request with the following: 

A new airport is under construction in N^qu, China in the northwest portion of the QinghaiTibet Plateau. The airport is scheduled for completion in 2010 and has a landing field elevation 

of 14,639 feet above sea level. The customer has requested the aircraft be capable of operations 

at this and other airports with field elevation above 14,000 feet (witii anticipated barometric 

pressure variations) up to 15,000 feet In order for the Model 680 Sovereign to provide the 

additional capability for landing at airports up to 15,000 feet pressure altitude, the Cabin Pressure 

Control System (CPCS) and Passenger Oxygen Control System (POCS) will be modified to 

allow the cabin internal pressure altitude to reach as higji as 15,150 +/-150 feet during ">14K" 

operations. Manual control of the oxygen system is not affected and can be activated at any time 

the crew deeir\s necessary. 

Public Interest Statement: 

Cessna's leadership position in the global business jet market is due to the efforts of its nearly 

8,000 employees in manuiacturing plants, completion centers, and service centers across the 

United States. This fiirthcr includes the many vendors located across the United States that 

provide the numeroiis aircraft pieces such as avionics, oxygen components, as well a the 

modified CPCS components that would be used for the aircraft to operate at this high elevation, 

Cessna competes for new business all over the world. Although the current economy has 

slowed, Cessna is striving hard to gain international markets for its business jets. This increased 

market directly affects the viability of Cessna and would aid in the stabilization of the job market 

as well as the growth of the American economy, which is directly in the interest of the public. 

Supporting Information: 

A requirement for automatic presentation of masks for airplanes certified to operate above 

30,000 feet originated in §4b-65I(d)(3)(i) of the Civil Aviation Regulations (CAR) and was 

carried over as §25.1447(c)(1) when part 25 was codified. The CAR requirement did not specify 

the maximum cabin altitude pressure allowed prior to presentation. The requirement that the 

oxygen equipment be automatically presented before the cabin pressure altitude reaches 15,000 

feet was added at Amendment 25-41, effective September 1,1977. This additional requirement 

recognized the hazard of oxygen deprivation on the average human being and its effect on 

carrying out actions under stressful conditions. 

The oxygen mask presentation at 15,750 +/- 250 feet is only selected ^^en a ">14K" switch is 

activated by the pilot. An indication light indicating that the aircraft is in ">14K" mode is also 

provided. This feature assists in limiting use of this mode to conditions when the airplane will 

operate from airfields with an elevation greater than 14,000 feet. The activation point for the 
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L390-10-0656 

Page 3 of3 

cabin altitude warning is also shifted with the same switch to avoid nuisance alerts when 

operating to and from airports at an altitude greater than 14,000 feet. Appropriate procedures 

will be provided in the Airplane Flight Manual to address proper operation of the ">14K" switch 

fimction. These features will have the flight crew select this fimction when descending to land at 

an airfield elevation greater than 14,000 feet and to reselect the ">14K" switch back to the 

"Normal" mode when climbing after takeoff from an airport with a field elevation greater than 

14,000 feet The procedure will minimize the time the aircraft is in the elevated altitude to that 

required to safely land and/or takeoff fixmi airports with a field elevation greater than 14,000 

feet. 

If you require additional information or have any questions, please do not hesitate to contact 

Donna DeBuhr at 316-517-0689, email ddcbuhr(3!cessna. textron.com 

Sincerely, 

/ -

Carlos Ayala 

TC ODA Administrator 

Cessna Aircraft Company 

ODA-100129-CE