68-12-06 ALLISON: Amdt. 39-612. Applies to Models 250-C18, 250-C18A, 250-C18B, 250-C18C, 250- C19 and 250-C10B engines.
Before further flight of any aircraft equipped with one of the Allison model engines listed above, unless already accomplished, modify the sixth stage compressor blades in these engines in accordance with Allison Commercial Engine Bulletin No. 250 CEB-48, dated June 11, 1968, or any other method approved by the Chief, Engineering and Manufacturing Branch, Central Region.
Further flight beyond the point where an aircraft equipped with one of these engines is grounded pursuant to this Airworthiness Directive, may be conducted only in accordance with Federal Aviation Regulation 21.197.
This amendment becomes effective June 18, 1968.