369/​500MD 500 · 530 · 600

MD Helicopters created rotating cone assemblies with new dash numbers but failed to identify them as life-limited parts, which could fail and cause loss of directional control. This AD establishes a 10,000-hour time-in-service life limit on these rotating cone assemblies.

Tail rotor blade pitch horns can crack due to corrosion under paint that causes premature fatigue failure, leading to loss of helicopter control. This AD requires inspecting pitch horns after paint removal for cracks, corrosion, and pitting, and establishing new retirement life limits with annual inspections.

Short-edge margin conditions on tailboom assemblies can lead to tailboom failure and loss of helicopter control. This AD requires measuring the distance between aft longeron rivets and outboard edge of frame rings, and installing a doubler if the distance is insufficient.

Moisture can degrade NOTAR fan blade tension-torsion straps over time, potentially causing loss of directional control. This AD requires determining cure dates for T-T straps, establishing retirement-life limits, reducing retirement life for certain straps, marking expiration dates, creating component records, and updating maintenance manual airworthiness limitations.

Failed adapter tubes on MD Helicopters Model 500N and 600N helicopters can cause loss of yaw control. This AD requires turning off the Yaw Stability Augmentation System, installing an airspeed limitation placard, revising the Rotorcraft Flight Manual, and replacing adapter tubes with airworthy ones that have a production date code stamp.

MD Helicopters Model 600N helicopters have issues with tailboom attachment fittings that require modification and repetitive inspection. Operators must modify the fuselage aft section, install inspection holes and bolt washers, modify access covers, and replace broken attachment bolts.

An abrasion strip separated from a tail rotor blade, which could cause vibration and loss of tail rotor control. This AD requires repetitive tap inspections of each tail rotor blade abrasion strip.

Landing gear struts may crack and fail, potentially causing loss of control during landing. This AD requires inspection of landing gear fairing support assemblies, replacement or reworking of certain forward and aft landing gear assemblies, creation of an access hole, and recurring inspections.

A tail rotor blade can fail due to improper bore conditions in the blade root fitting, potentially causing loss of control. Before flight, remove and inspect each tail rotor blade assembly for a smooth radius bore, replacing any defective blades and marking serviceable ones with the helicopter model.

Fuel nozzle screens can contaminate and collapse, causing sudden loss of engine power and uncommanded shutdown. This AD requires inspection of the fuel nozzle screen for contamination and replacement of affected fuel nozzles with a new design, with cleaning of the aircraft fuel system if contamination is found.

MD Helicopters main rotor blades are susceptible to fatigue cracking that could lead to blade failure and loss of helicopter control. The AD requires recording torque events, inspecting blade surfaces for cracks, and replacing cracked blades with airworthy ones.

The control support bracket on certain Model 600N helicopters has a shorter fatigue life than originally analyzed, risking bracket failure and loss of control. This AD requires replacing the control support bracket, reducing its life limit, and revising the maintenance manual with updated life limits.

Forward and center thruster control cable assembly connectors on certain MD Helicopters 500N and 600N helicopters may suffer corrosion pitting or cracking, potentially causing cable failure and loss of control. This AD requires inspection of both connectors using bright light and 10x magnification, with replacement of any defective cable assemblies before further flight.

The main rotor drive shaft on certain MD Helicopters 600N models is subject to fatigue failure that could cause loss of main rotor drive and helicopter control. This AD reduces the drive shaft life limit by 2000 hours and requires updating the component history card with the new limit.

Tail rotor gearbox bolts may have inadequate grip length, risking gearbox loss and loss of helicopter control. This AD requires identifying and replacing inadequate bolts with airworthy ones, adding washers if necessary, and reapplying slippage marks after torque testing.

Breeze Eastern Aerospace rescue hoists have experienced cracked mounting brackets that could separate the hoist from the helicopter. Perform a one-time inspection of mounting brackets for cracks and replace with serviceable parts if necessary.

Main rotor blade skin-to-spar bonding voids can allow corrosion pits to develop on blade spar surfaces, leading to blade failure and loss of control. The AD requires a one-time tap inspection of both surfaces of each main rotor blade before further flight, and replacement of any unairworthy blade before flight.

MD Helicopters helicopters with certain analog/digital turbine outlet temperature indicators have shown erroneous readings and wiring harness defects that can damage engine components and cause loss of power. The AD requires repetitive calibration testing of the TOT indicating system and corrective actions if necessary.

Stress corrosion cracks have been found on thruster control cable conduit caps, which could cause loss of anti-torque directional control. Operators must inspect the caps for corrosion or cracks within 5 hours time-in-service or before December 31, 1999, and again within 100 hours or before February 19, 2000, replacing any unacceptable caps.

Three oil cooler blower brackets have cracked, risking loss of engine and transmission oil cooling and forced landing. This AD requires replacing the affected bracket.

Fatigue testing revealed that several life-limited pitch control components need shorter service lives to prevent failure. The AD requires applying serial numbers to these components and replacing them according to new life limits.

Certain tail rotor fork assemblies may fail, causing loss of a tail rotor blade and loss of helicopter control. Operators must inspect and replace defective fork assemblies before flight, then perform repetitive inspections every 50 hours.

Pitting has been discovered on internal spline teeth of certain input shaft coupling assemblies, which could lead to failure and loss of main rotor drive. Operators must perform a one-time visual inspection of affected coupling assemblies for pitting.

Certain Allison Engine Company 250-B and 250-C series engines can experience leaking main fuel control bellows assemblies, causing uncommanded minimum fuel flow and loss of engine fuel flow control. This AD requires replacing beryllium copper MFC bellows assemblies with Inconel 718 stainless steel welded MFC bellows assemblies.

Overrunning clutch assemblies may experience bearing wear from spinning of the bearing outer race, causing inflight vibrations and potential loss of rotor drive. Perform visual inspections of the clutch retainer, carrier, housing, and pin for wear.

AlliedSignal KT 76A ATC transponders with certain serial numbers are transmitting misleading altitude information to ATC radar and TCAS-equipped aircraft. This AD requires replacing two resistor network modules with glass-coated modules on affected transponders.

Main rotor blades on these helicopter models have experienced fatigue cracks that could lead to blade failure and loss of control. Operators must inspect blades for cracks and missing or cracked adhesive or paint, record torque events, and retire certain blades per the AD's schedule.

Tail rotor control rod assemblies may buckle under ultimate jam loads, causing loss of tail rotor control. The AD requires removing and replacing the tail rotor control rod assembly with an airworthy unit.

Overrunning clutch outer races can fail due to heat treatment defects, causing loss of engine drive to the rotor system and forcing a landing. Replace all outer races with airworthy replacements regardless of heat treatment number.

Transmission output drive gears in certain McDonnell Douglas helicopters are subject to spalling or fracture, particularly during high-power or external-lift operations, which can result in loss of main rotor control. This AD requires replacement of the affected transmission output drive gears.

Allison 250 series turbine engines with Superior Air Parts PMA bearings may experience bearing separator instability leading to bearing failure and subsequent turbine and engine damage. The AD requires initial and repetitive visual inspections of engine filters for metal particles and replacement of the affected bearings with improved units.