Is AD 99-25-08 a recurring Airworthiness Directive?

No — AD 99-25-08 is a one-time directive. Verify it was complied with in the aircraft's records.

Which aircraft does AD 99-25-08 apply to?

AD 99-25-08 applies to Md Helicopters — models 500N, 600N. Serial/part conditions may narrow it to specific aircraft.

Airworthiness Directive 99-25-08

one-time

Official AD 99-25-08 · FR doc 00-3222 · 2000-02-15 · airframe

Airworthiness Directives; MD Helicopters Inc. Model 500N and 600N Helicopters

What this AD requires

This document publishes in the Federal Register an amendment adopting Emergency Priority Letter Airworthiness Directive (AD) 99-25- 08, which was sent previously to all known U.S. owners and operators of MD Helicopters Inc. (MDHI) Model 500N and 600N helicopters by individual letters. This AD requires, within the next 5 hours time-in- service (TIS) or before further flight after December 31, 1999, whichever occurs first, inspecting the thruster control cable conduit cap (cap) for corrosion or a crack. This AD also requires, within the next 100 hours TIS or before further flight after February 19, 2000, whichever occurs first, inspecting the cap at a specified area of the forward and center thruster cables for corrosion or a crack. If an unacceptable crack is found, replacing the unairworthy thruster cable with an airworthy thruster cable is required. This amendment is prompted by the discovery of stress corrosion cracks on an MDHI Model 500N helicopter. The actions specified by this AD are intended to prevent failure of the cap causing a fixed thruster condition and subsequent loss of normal anti-torque directional control of the helicopter.

Which aircraft AD 99-25-08 applies to

MakesMd Helicopters

Models500N, 600N

Part-conditional — 500N7201-5, 500N7201-7, 500N7201-37, 500N7201-45, 500N7201-51, 500N7201-55, 500N7201-57, 500N7201-59.

Inspect/replace forward and center thruster (NOTAR anti-torque) control cables per MDHI SB500N-021/SB600N-028 and SB500N-020R1/SB600N-027R1; terminating action installs cable P/N 500N7201-55/-57 on Model 500N or 500N7201-55/-59 on Model 600N.

Whether AD 99-25-08 actually applies to your aircraft (by serial and installed parts) and whether it’s already complied with comes from that aircraft’s records.

How AD compliance is recorded

A valid compliance record (14 CFR 43.9) states:

Method of compliance — The specific action taken (inspected, replaced, modified) and to what revision.

Date — When the work was done.

Aircraft time — Total time in service / tach at compliance — how recurring next-due is computed.

Signature & certificate — The A&P/IA who returned it to service, with certificate number.

Is AD 99-25-08 complied with on your aircraft?

Tailplate reads a tail number’s logbooks and matches every applicable AD — including this one — to its compliance evidence, with recurring next-due dates computed.

Look up a tail number →Read the full directive (Federal Register)

Applicability is derived from the FAA directive corpus and is advisory, not a legal airworthiness determination. Compliance is established only from an aircraft’s actual records.