Department Number

C8020 Northwest Airlines, Inc. 5101 Northwest Drive St. Paul, MN 55111-3034

June 28, 2002

federal Aviation Administration Transport Airplane Directorate, ANM-114 Attention: Rules Docket No. 2002-NM-12-AD Seattle Aircraft Certification Office 1601 Lind Avenue SW Renton, WA 98055-4056 

### NORTHWEST AIRLINES



# RECEIVED
JUN282002 

## ANM -114

Subject:

Reference: Comments to Docket No. 2002-NM-12-AD

(A) NPRM Docket No. 2002-NM-12-AD (B) Boeing Service Letter 757-SL-24-069 (C) Boeing Service Letter 747-SL-24-058 (D) Avionic Instruments Inc. Service Bulletin 1-002-0102-1000-24-24

The FAA issued referenced (A) NPRM 2002-NM-12-AD proposing the adoption ofa new airworthiness directive (AD) that would require the modification ofspecific static inverters to prcvent an overheating condition caused by aresistor within the inverter. The NPRM identifies

an incident where the resistor overheated burning surrounding capacitors causing smoke inthe flight deck. Thc NPRM isproposing that the modification be accomplished within 18months of the effective date. NWA's Boeing 757-200/300 and 747-400 aircraft currently operate with the referenced static inverters. The following are NWA's comments regarding the referenced (A) NPRM Docket:

Item #IDiscussion: Under the discussion paragraph, the NPRM identifies that analysis conducted by the manufacture ofthe static inverter identified that the proximity ofthe R170resistor to capacitors C50 and C51 could lead to overheating and possible damage or failure ofthe referenccd capacitors. Furthermore, the paragraph indicates that the manufacturc's analysis suggests that the combination ofobstructed convcction cooling and localized heat from RI70 resulted in sufficient energy to damage the adjacent capacitors. NWA's engineering group contactcd the static inverter manufacturer's repair dcpartmcnt and found that while the manufacturer agreed with thc assessment that the R170resistor was the source ofenergy that damaged the rcfcrenced capacitors, the manufacturer was conccrned that morc recent evidence indicates that aliquid suhstanee may have leaked on to the resistor and contributed tothe R170resistors' overheating condition.

N\VA is concerned that the root cause ofthe resistor's overheat condition my not be accurately addresscd, and that this NPRM may be more symptomatic innature. NWAisrequesting confirmation as to the cause of the referenced Rl70 resistor's overheating condition. Ifthe
cause ofthe Rl70 resistor's excessivc over heat condition isfound to be due to a liquid spill/lcak, NWA would recommend that the NPRM bc withdrawn, orat aminimum the compliance time bc relaxcd to4ycars to avoid unduc hardsbip on the airlines.Item #2 Cost Impact:

The NPRM Cost impact paragraph states that, " the FAA has been advised that manufacturer warranty remedies are available forthe cost ofthe modified replacement parts and labor associated with accomplishing the actions specified by this AD. Therefore, the economic cost impact ofthis proposed AD on U.S. operators may be minimal." Per the referenced (D) service bulletin and confirmation from the manufacturer, all units driven into the manufacturer's repair facility specifically forthis modification will be responsible forre-certification charges. These re-certification charges equate to approximately 5550.00 per unit. NWA operates approximately forty ofthe suspect static inverters. The manufacturer has indicated that units returned for normal repair or service will automatically be upgraded atno re-certification cost. NWAis requesting that the referenced paragraph identify the re-certification charges for the accomplishment ofthe AD.

Item #3 Applicability Table: PerTable Iunder the Applicability paragraph, aircraft model and series information relative to the specific static inverter part number isnot consistent with referenced (B) & (C) Boeing service letters. For example, Table I ofthe NPRM implies that part number 1-002-0I02-0265 is used on the Boeing 737 series aircraft only, while the referenced (B) & (C) Boeing service letters indicate that the referenced part number isused on the 737 and 747-400 series aircraft. NWAisrequesting clarification as to which table has the correct applicability information.

Item #4 Applicability Table: Per the manufacture, part number 1-001-0102-0265 also requires the referenced resistor modification. This part number is not identified inany ofthe referenced documentation. NWA isrequesting clarification as to whether part number 1-001-0102-0265 is tobe included into the applicability tables.
Respectfully.

Mark Millam Chief Engineer

cc: K. Hylander R. Gleason D. Lee G. Budinger R. Fox D. Bowling J. Marcolina W. Branz