Airworthiness Directive · Amendment 39-17121 · Rotorcraft servo system
Bell Helicopter Textron Canada Helicopters
This AD applies to the following helicopters, certificated in any category:
(1) Model 407 helicopters, serial numbers (S/Ns) 53000 through 53900, 53911 through 53999, and 54000 through 54081, with a hydraulic servo actuator assembly (servo) part number (P/N) 206-076-062-105 or P/N 206-076-062-107; and
(2) Model 427 helicopters, S/Ns 56001 through 56077, 58001, and 58002, with a servo, P/N 206-076-062-109 or P/N 206-076-062-111.
We are adopting an airworthiness directive (AD) superseding an existing airworthiness directive for Bell Helicopter Textron Canada (Bell) Model 407 and 427 helicopters. The existing AD requires inspecting certain hydraulic servo actuators (servo) to determine whether the shaft turns independently of the nut or the clevis assembly, and additional actions based upon the inspection's outcome. The AD also requires reidentifying the servo. Since we issued that AD, Bell has learned that additional servos may need repair or removal. This AD expands the scope of the current AD to include inspections for all servos, and requires that servos meeting inspection requirements be marked with the letter "V" after the part number on the data plate. The actions are intended to detect any loose or misaligned parts in the servo that could lead to failure of the servo and subsequent loss of helicopter control.
You are responsible for performing each action required by this AD within the specified compliance time unless it has already been accomplished prior to that time.
(1) Before further flight, conduct a one-time visual inspection of the servo by doing the following:
(i) Retract the boot depicted as 230 in Figure 1 to Paragraph (f) of this AD.
(ii) Applying only hand pressure, determine whether the nut, the shaft, or the clevis assembly, depicted as items 225, 215 and 205, respectively, in Figure 1 to Paragraph (f) of this AD, turn independently. If the shaft turns independently of the nut or clevis assembly, before further flight, replace the servo with an airworthy servo.
(iii) If the shaft does not turn independently, inspect to determine if at least one tab of the lock washer is bent flush against a flat surface of the nut and if at least one tab of the lock washer is bent flush against a flat surface of the clevis assembly.
(iv) If at least one lock washer tab is not aligned and bent flush with a nut flat surface and at least one lock washer tab is not aligned and bent flush with a flat surface of the clevis assembly, before further flight, replace the servo with an airworthy servo.
(v) If any tab of the lock washer is not bent flush against either a flat surface of the nut or clevis assembly, bend the tab flush against a flat surface.
(2) After accomplishing paragraphs (f)(1)(i) through (f)(1)(v), vibro-etch the letter “V” at the end of the part number on the data plate.
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.
