Is AD 77-13-20 a recurring Airworthiness Directive?

No — AD 77-13-20 is a one-time directive. Verify it was complied with in the aircraft's records.

Which aircraft does AD 77-13-20 apply to?

AD 77-13-20 applies to Bristol — models MK.522, MK.601-22, Viper. Serial/part conditions may narrow it to specific aircraft.

Airworthiness Directive 77-13-20

one-time

AD 77-13-20 · 1977-01-01 · turbine engine

Airworthiness Directives; for installation, on Hawker Siddeley Model DH/BH-125 series airplanes, certificated in all categories. Compliance is required as i

Which aircraft AD 77-13-20 applies to

MakesBristol

ModelsMK.522, MK.601-22, Viper

Applies to Bristol Viper MK.522 and MK.601-22 engines installed, or being held for installation, on Hawker Siddeley Model DH/BH-125 series airplanes, certificated in all categories; requires realigning the fuel tube for adequate clearance; effective per Amendment 39-2945.

Whether AD 77-13-20 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 77-13-20 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 →

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.