Airworthiness Directive · Amendment 39-17659 · Fuselage
The Boeing Company Airplanes
This AD applies to The Boeing Company Model 737-600, -700, -800, -900, and -900ER series airplanes, with passenger seats installed; certificated in any category; as identified in Boeing Special Attention Service Bulletin 737-53-1296, dated January 11, 2011.
We are adopting a new airworthiness directive (AD) for certain The Boeing Company Model 737-600, -700, -800, -900, and -900ER series airplanes. This AD was prompted by reports that certain seat track bolts were found with severed head bolts due to fatigue. This AD requires replacing titanium seat track bolts with corrosion resistant steel (CRES) bolts, repetitive inspections for cracking of the splice strap and forward seat track holes, and related investigative and corrective actions if necessary. This AD also provides an optional terminating action for the repetitive inspections. We are issuing this AD to detect and correct missing or severed bolt heads, which, if not corrected, could result in the inability of the seat track to carry passenger loads, which could cause the seats to detach from the seat track, resulting in possible injury to passengers during an emergency landing or survivable crash.
Before the accumulation of 7,000 total flight cycles, or within 24 months after the effective date of this AD, whichever occurs later: Replace titanium seat track bolts with corrosion resistant steel (CRES) bolts at both the left and right sides of buttock lines 24.75 and 45.50, in accordance with the Accomplishment Instructions of Boeing Special Attention Service Bulletin 737-53-1296, dated January 11, 2011. If a titanium seat track bolt is found missing from the structure during the accomplishment of the tasks required by paragraph (g) of this AD: Before further flight, do a high frequency eddy current (HFEC) inspection for cracking in the fastener holes and a general visual inspection of the area, including the splice strap and forward seat track for damage, and replace missing bolts with new or serviceable CRES bolts, in accordance with the Accomplishment Instructions of Boeing Special Attention Service Bulletin 737-53-1296, dated January 11, 2011. If cracking or damage is found: Before further flight, repair the seat track using a method approved in accordance with the procedures specified in paragraph (j) of this AD. If it is necessary to remove more parts for access, those parts may be removed. If access can be obtained without removing identified parts, it is not necessary to remove all identified parts. Jacking and shoring limitations should be observed.
Before the accumulation of 7,000 total flight cycles, or within 24 months after the effective date of this AD, whichever occurs later: Do a detailed inspection and an HFEC inspection for cracking in the holes common to the splice strap and forward seat track at both the left and right sides of buttock lines 24.75 and 45.50, in accordance with the Accomplishment Instructions of Boeing Special Attention Service Bulletin 737-53-1296, dated January 11, 2011. Repeat the inspections thereafter at intervals not to exceed 7,000 flight cycles, until the actions specified in paragraph (i) of this AD have been done.
(1) If a crack is found in the splice strap during any inspection required by paragraph (h) of this AD: Before further flight, replace the seat track bolts and install a new splice strap part number (P/N) 146A5342-26 and retained angle at the affected location, in accordance with the Accomplishment Instructions of Boeing Special Attention Service Bulletin 737-53-1296, dated January 11, 2011.
(2) If a crack is found in the seat track during any inspection required by paragraph (h) of this AD, and Boeing Special Attention Service Bulletin 737-53-1296, dated January 11, 2011, specifies to contact Boeing for appropriate action: Before further flight, repair the seat track using a method approved in accordance with the procedures specified in paragraph (j) of this AD.
Replacing the titanium seat track bolts with CRES bolts on both the left and right sides of buttock lines 24.75 and 45.50 at station 727B, and installing a new splice strap P/N 146A5342-26, in accordance with the Accomplishment Instructions of Boeing Special Attention Service Bulletin 737-53-1296, dated January 11, 2011, terminates the repetitive inspections required by paragraph (h) of this AD.
Note 1 to paragraph (i) of this AD: Boeing Special Attention Service Bulletin 737-53-1296, dated January 11, 2011, contains an error in Step 1, “Move,” of Figure 10, Sheet 5 of 7; and in Step 1, “Move,” of Figure 12, Sheet 5 of 7. The splice strap needs to be centered with left buttock line 45.50 and right buttock line 45.50, respectively— not left buttock line 24.75, as stated in that service bulletin.
