Airworthiness Directive · Amendment 39-11753 · Air Tractor Incorporated Models AT-301, AT-401, and AT-501 Airplanes
Air Tractor Incorporated Models AT-301, AT-401, and AT-501 Airplanes
The following airplane models and serial numbers that are:
(1) Certificated in any category; and
(2) Equipped with a 3/16 -inch fin front spar fitting and an all metal rudder.
| Models | Serial numbers |
|---|---|
| AT-301 | 301-0100 through 301-0736 |
| AT-401 | 401-0662 through 401-0736 |
| AT-501 | 501-0002 through 501-0030 |
Note: This AD does not affect the requirements of AD 97-14-05, Amendment 39-10063 (62 FR 38445, July 18, 1997). AD 97-14-05 requires similar actions to this AD on Models AT-302, AT-400, AT-400A airplanes, and certain Models AT301, AT-401, and AT-501 airplanes that are not affected by this AD.
This amendment adopts a new airworthiness directive (AD) that applies to certain Air Tractor Incorporated (Air Tractor) Models AT- 301, AT-401, and AT-501 airplanes that are equipped with a \3/16\-inch thick aluminum fin front spar fitting and an all metal rudder. This AD requires that you repetitively inspect the vertical fin front spar attachment fittings for fatigue cracks, and rework the vertical fin if any cracks are found. This AD is the result of reports of a vertical fin front spar fitting failure on a Model AT-401 airplane. The actions specified by this AD are intended to detect and correct cracks in the vertical fin front spar attachment fittings, which could result in failure of the vertical fin. This condition could lead to loss of directional control and eventual loss of airplane control.
To address this problem, you must accomplish the following:
| Action | Compliance time | Procedures |
|---|---|---|
| (1) Initial inspection of the fin front spar attachment fittings for fatigue cracks | At whichever of the following that occurs later (i) Upon accumulating 4,000 hours time-in-service (TIS); or, (ii) Within the next 25 hours TIS after the June 23, 2000 (the effective date of this AD) | Accomplish in accordance with the Inspection Requirements section of Snow Engineering Company Service Letter #138, Issued July 29, 1995; Revised August 7, 1996. |
| (2) Repetitive inspections of the fin front spar attachment fittings. Repetitive inspection requirement only applies if no cracks are found and you choose not to rework the fin front spar attachment | Within 100 hours TIS after the initial inspection and thereafter at intervals not to exceed 100 hours TIS if you have no cracks and choose not to rework the fin front spar attachment | Accomplish in accordance with the Inspection Requirements section of Snow Engineering Company Service Letter #138, Issued July 29, 1995; Revised August 7, 1996. |
| (3) Rework the fin front spar attachment fittings | (i) Prior to further flight after any inspection where a crack is found in the front or rear spar area (ii) This eliminates the repetitive inspection requirement of this AD | Accomplish in accordance with the Vertical Fin Rework Instructions section of Snow Engineering Company Service letter #196, Issued February 9, 2000; Revised March 7, 2000. |
| (4) Optional rework of the fin front spar attachment fittings | Any time to eliminate the repetitive inspection requirement of this AD | Accomplish in accordance with the Vertical Fin Rework Instructions section of Snow Engineering Company Service Letter #196, Issued February 9, 2000; Revised March 7, 2000. |
Note: The applicability of Snow Engineering Company Service Letter #138 refers to different airplanes than are referenced in this document. AD 97-14-05, Amendment 39-10063 (62 FR 38445, July 18, 1997), covers the airplanes referenced in Snow Engineering Company Service Letter #138. The inspection procedures also apply for the airplanes referenced in this AD. Therefore, Snow Engineering Company Service Letter #138 also applies to this AD, as well as AD 97-14-05. This service letter also specifies repetitive inspection intervals of 25 hours TIS. Paragraph (d)(2) of this AD requires the repetitive inspections at 100 hours TIS.
The aircraft, engines and makers this AD names, by the model designations in its text. A model listed here may still be outside the AD's serial ranges.
