Delta Air Lines

SUMMARY: The Ref (A) proposed rule would require operators to repetitively test the takeoff warning system to detect potential failures of the "NOSE UP STAB TAKEOFF WARNING SWITCH" S132, and "NOSE DOWN STAB TAKEOFF WARNING SWITCH" S546. Failure of one or both of these switches could result in the horizontal stabilizer set out of the takeoff range without a takeoff configuration aural warning. This condition could reduce the ability of the flight crew to control the aircraft. These actions are to be accomplished in accordance with Boeing Alert Service Bulletin 737-27-1289. The proposed rule would be applicable to 737-600, -700, -800, -900, and -900ER aircraft as listed in SB 737-27-1289. The rule as proposed affects 71 Delta 737-800 aircraft and 10 DAL 737-700 aircraft. DELTA’S COMMENTS Summary Delta concurs that the proposed action is required. After reviewing the proposed rule, Delta suggests the inclusion of an additional replacement switch part number and notes that the actual cost to operators will be more than described in the cost of compliance given in the NPRM preamble. Comments Regarding Inclusion of Additional Replacement Switch Part Numbers DAL suggests that the final rule allow for switch P/N 35EN27-4 to be an additional acceptable replacement switch. Paragraph (h) of the proposed rule specifies that any stabilizer takeoff warning switch which fails the required test must be replaced with a new switch prior to further flight. The switch is to be replaced in accordance with SB 737-27-1289. SB 737-27-1289 Section 3.B 'Work Instructions' do not specify replacement switches by part number. Replacement switch part numbers are found in Section 2.C.2 'Parts and Materials Supplied by the Operator' of the SB. This section lists only three (3) part numbers for replacement switches, specifically P/N 32EN14-4, P/N 32EN21-4, and P/N 32EN61-4. DAL is aware of an additional switch which is not listed in SB 737-27-1289 Section 2.C.2. This switch is