Is AD 99-683 a recurring Airworthiness Directive?

Yes — AD 99-683 requires a repetitive inspection every 150 hours. Next-due depends on the aircraft's time in service.

Which aircraft does AD 99-683 apply to?

AD 99-683 applies to Mcdonnell Douglas — models MD900. Serial/part conditions may narrow it to specific aircraft.

Airworthiness Directive 99-683

recurring

AD 99-683 · 1999-01-19 · airframe

Airworthiness Directives; McDonnell Douglas Helicopter Systems Model MD-900 Helicopters

What this AD requires

This document publishes in the Federal Register an amendment adopting Airworthiness Directive (AD) 98-12-30 which was sent previously to all known U.S. owners and operators of McDonnell Douglas Helicopter Systems (MDHS) Model MD-900 helicopters by individual letters. This AD requires inspecting the main rotor upper hub assembly (hub assembly) for cracks, and if a crack is found, replacing the hub assembly. The AD also requires verifying attachment nut torque values and a repetitive inspection at intervals not to exceed 150 hours time- in-service. This amendment is prompted by the discovery of cracks in 6 main rotor upper hub assemblies. This condition, if not corrected, could result in failure of the hub assembly, loss of drive to the main rotor, and subsequent loss of control of the helicopter.

Repetitive inspection. Re-inspect every 150 hours. The next-due date/hours depend on this aircraft’s time in service — a records report computes it from the logbooks.

Which aircraft AD 99-683 applies to

MakesMcdonnell Douglas

ModelsMD900

Main rotor hub assembly and drive plate; inspect hub bolt-hole area for cracks and replace attachment hardware (10 bolts/nuts/20 washers) with new sets; torque to 160-180 in-lbs above locknut run-on torque. Model inferred from Boeing McDonnell Douglas Helicopter Systems Service Letter SL900-039 numbering (MD900 series).

Whether AD 99-683 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 99-683 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.