AmericanAirlines 

MAINTENANCE & ENGINEERING CENTER 

^^RTMENTO 

November 23, 2010 . ^i'^SPORTATlON 

^AciOPFRATiONS 

U. S. Department of Transportation 

Docket Operations ' iO f'QV 2 b A iO- 38 

West Building Ground Floor, Room W12-140 

1200 New Jersey Avenue, SE. 

Washington DC, 20590 

Subject: Request for Exemption to Sections of 14 CFR Parts 121, and 121.344(f): 

American Airtines, Inc. v^^ould like to petition the Federal Aviation Administration for a timelimited exemption of 18 months from December 6, 2010, to 14 CFR 121.344 to continue 14 CFR 

121 operations of four 737-823 series aircraft using a flight data recorder system that does not 

fully comply with the recording interval requirements for the left elevator surface position 

parameter, also known as "Primary pitch control surface position." 

Applicable Sections: 

This exemption request only involves parameter "(15) Primary pitch control surface position" as 

listed in 14 CFR 121.344 paragraph (a). 

14 CFR 121.344 (f) states Tor all turbine-engine-powered transport category airplanes that are 

manufactured after August 19, 2002.(1) The parameters listed in paragraph (a) (1) through (88) 

of this section must be recorded within the ranges, accuracies, resolutions, and recording 

intervals specified in Appendix M of this part". 

14 CFR 121.344 Appendix M (Note 18) states "For all aircraft manufactured on or after 

December 6, 2010, the seconds per sampling interval is 0.125. Each input must be recorded at 

this rate. Alternately sampling inputs (interleaving) to meet this sampling interval is prohibited". 

Extent of Relief 

This time-limited exemption would allow for the continued domestic and international operations 

of the following American Airlines operated B737-823 series aircraft (see Table 1) for 18 months 

after December 6, 2010, without the fully compliant recording interval of the left elevator surface 

position parameter (See Table 2): 

Make / Model 

Boeing / 737-823 

Boeing / 737-823 

Boeing / 737-823 

Boeing / 737-823 

Table 1 (Aircraft Applicable to this Exemption) 

Serial # 

30903 

31111 

29554 

40584 

Line# 

3481 

3487 

3493 

3499 

Reaistration # 

N863NN 

N864NN 

N865NN 

N866NN 

Table 2 

121.344(f) 

Parameter # 

15 

(System Signals not recorded 

Appendix M 

Reauirement 

Pitch Control 

Surface Position 

by the Digital Flight Data Recorder) 

Inout to DFDAU 

Left Elevator Position Data 

(1 sample of the 8 Hz set 

every 5 seconds) 

Page 1 of 4 

MD P.O. BOX 582809, TULSA, OKLAHOMA 74159-2809, CABLE ADDRESS AMAIR 
American Airlines - 737NG Exemption Request 

November 23, 2010 

Reason for relief 

This exemption is necessitated by the Aircraft Manufacturer (Boeing) and the Digital Flight Data 

Acquisition Unit (DFDAU) system / software supplier's (Teledyne) need to develop, validate, and 

integrate the enhanced system software into the aircraft type design. This enhanced software 

will provide for the DFDAU recording of all regulatory required parameters and allow American 

Airlines time to install the software without significantly affecting flight operations. 

Background 

Summary: 

A 737NG Flight Data Recorder System (FDRS) anomaly was discovered during Boeing flight 

line airplane operations. The FDRS configuration included a Teledyne Digital Flight Data 

Acquisition Unit (DFDAU) with the 737-7 data frame enabled. The data frame is a 512 words 

per second data frame that was certified in April of 2010 to meet the latest FAA regulations (§ 

121.344 (f) Appendix M), which are effective Dec 6, 2010. The following describes the anomaly 

and discusses Boeing's plan to correct the discrepancy. 

Discussion: 

On 10/19/2010, an anomaly was reported on a Boeing production 737NG airplane. This detailed 

a problem with the display of the left elevator position on the Center Lower Display Unit which 

was lagging when compared to the right elevator position on that display. The Common Display 

System (CDS) retrieves surface position data from the DFDAU for optional flight crew display. 

The display of elevator position is NOT required to meet certification regulations and supports 

an optional Maintenance Ground Operation to aid in airplane dispatch. The display of the 

elevator positions (along with other primary flight control positions) on the CDS is a customer 

option. When the anomaly was reported. Flight Data Recorder (FDR) data was downloaded 

and analyzed to determine if the problem seen on the CDS was also present in the FDR 

elevator position data. Per FAA regulations (§ 121.344 (f) Appendix M (parameter group 15)), 

as of Dec 6, 2010 the FDRS must record left and right elevator position at 8 samples per 

second. 

FDR data analysis showed that at times, 1 of the 8 samples of left elevator position data, in a 

given second, could be stale (a previous sample) and is visible if there is a rapid movement of 

the elevator position. The anomalous left elevator position data is usually present only once 

every 5 seconds (i.e. once every 5 seconds there are only 7 valid samples and one invalid 

sample in a one second acquisition period (Sub frame)). Right elevator position data was 

shown not to be effected by the anomaly. It is possible to deduce a corrected left elevator 

position sample from comparison of this parameter to the right elevator position and linear 

interpolation between correct left elevator position samples around the anomaly. The operation 

of the right and left elevators typically track the movement of each other due to the mechanics of 

the elevator system. In summary, this anomaly can be addressed in ground processing of the 

data. 

The root cause of this anomaly is found in a DFDAU software acquisition timing error. 

Periodically, in a given parameter acquisition cycle, the DFDAU is requesting the acquisition of 

more parameter data than it has time to complete in that acquisition cycle. Because parameter 

acquisition does not have time to complete the previous valid sample is used in the recording 

rather than the desired current sample. 

Page 2 of 4 
American Airlines - 737NG Exemption Request 

November 23, 2010 

The DFDAU software is software loadable and Teledyne has informed Boeing that this anomaly 

can be fixed with a minor software revision resulting in new software part numbers. 

Plan to Correct Anomaly: 

Boeing has verbally notified the FAA and is in the process of filing a "Report of Noncompliance 

with Part 25 Ainworthiness Regulations" with the FAA stating that the anomaly does not 

represent a safety issue for continued operation. 

Boeing has a pending contract in-work with Teledyne and after its acceptance the plan is to 

certify the new DFDAU software in approximately 5-6 months. The date of certification is 

contingent on what is found during test which may cause the schedule to move either left or the 

right. In any case, Boeing is actively working to accelerate the certification of corrected 

software. 

Upon receipt of the Boeing Service Bulletin and certified software, American Airtines will install 

this software within 90 days, terminating the need for the exemption. 

Public Interest 

The granting of this exemption would be in the public interest by allowing American Airlines to 

continue providing service to domestic and international destinations utilizing the B737-823 

series aircraft listed in Table 1. 

Failure to grant this exemption would require American Airlines to cancel flights and disrupt 

schedules causing significant financial loss as well as impose inconvenience and potential losttime cost to the traveling public. 

Affect on the Level of Safety 

The fact that the FDRS is missing 1 recorded sample every 5 seconds does not have an 

adverse affect on the normal or irregular operation of the aircraft. It is possible to deduce a 

corrected left elevator position sample from comparison of this parameter to the right elevator 

position with linear interpolation. The operation of the right and left elevators typically track the 

movement of each other due to the mechanics of the elevator system. In summary, this 

anomaly can be addressed in ground processing of the data. The manufacturer of the aircraft 

(Boeing) has reviewed this exemption and has determined "the issue is not considered to be a 

risk to current and future operation of the airplane." 

Summary for the Federal Register 

As described in 14 CFR 11.87, American Airlines requests that this exemption not be published 

in the Federal Register and follow with request for comments due to the ensuing delay of 

potentially granting the exemption. 

American Airtines is requesting an exemption from 14 CFR Part 121.344 to allow for the 

continued operation of B737-823 series aircraft in domestic and international revenue service 

without the installed Digital Flight Data Acquisition Unit (DFDAU) recording all 8 samples of the 

left elevator position data. This exemption shall allow the Aircraft Manufacturer (Boeing) and 

the DFDAU System Software Provider (Teledyne) time to develop, validate, and certify the 

software to correct the DFDAU anomaly and allow American Airtines time to install the software 

with minimal interruption to flight scheduling. 

Page 3 of 4 
American Airlines - 737NG Exemption Request 

November 23, 2010 

Additional Information 

Boeing has verbally notified the FAA and is in the process of filing a "Report of Noncompliance 

with Part 25 Airworthiness Regulations" with the FAA stating that the anomaly does not 

represent a safety issue for continued operation. 

Use of the Exemption outside the United States 

American Airiines would like to utilize the privileges of this exemption outside the United States. 

The primary scheduled operations for this model aircraft in American Airiines fleet includes 

international operations primarily in Mexico, Canada, Central America, South America and the 

Caribbean. 

Your consideration of the foregoing and expedited approval of this request is appreciated. If you 

have any questions regarding this request, please fee! free to contact this office. 

Sincerely, 

William M. Cavitt 

Vice President Engineering, Performance & 

Quality Assurance 

On behalf of: American Airiines, Inc. 

Air Carrier Certificate AALA025A 

3900 N Mingo Rd,MD 183 

Tulsa, OK 74116 

Phone: 918-292-2902 

Fax: 918-292-1830 

Email: bill.cavitt@aa.com 

cc: Federal Aviation Administration 

AAL Certificate Management Office 

c/o Mr. William T. Satterfield, PAI 

14800 Trinity Blvd, St. 100 

FortWorth, Texas 76155 

The Boeing Company 

B. C. Groenewegen, 

Manager, Continued Ain/vorthiness 

Twin Aisle Programs 

P.O. Box 3707 

Seattle WA 98214-2207 

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