71-16-04: Battery Change or Modification of Comb

71-16-04 LEARJET: Amdt. 39-1255. Applies to Models 23 (S/N 23-003 through 23- 099); 24 (S/N 24-100 through 24-247); and 25 (S/N 25-002 through 25-080) Airplanes. Compliance: Required as indicated, unless already accomplished. To prevent battery temperature and charging conditions that can result in battery fires and in intense heat, accomplish the following: A) Prior to the next flight conduct a one-time inspection of both batteries for: 1) Heat damage, and if any heat damage is found, replace the damaged battery with an airworthy one. 2) The presence of marathon (sonotone) batteries, Model CA20H or CA21H and for the type of cells (polystyrene, nylon or a combination thereof) contained in said batteries. NOTE: Polystyrene cells can be identified by their clear or slightly yellow plastic appearance. All marathon batteries manufactured prior to 1969 contained polystyrene cells. Marathon batteries manufactured in 1969 or later, contain nylon cells which are identifiable by their milky white or bluish appearance. All marathon batteries rebuilt since new may contain a mixture of polystyrene and nylon cells. B) Within ten (10) hours' time in service after the effective date of this AD, on those aircraft having marathon (sonotone) batteries Models CA20H or CA21H containing either all polystyrene cells or a combination of polystyrene and nylon cells, and within fifty (50) hours' time in service after the effective date of this AD and on those aircraft having other approved batteries or sonotone batteries containing all nylon cells install Learjet Modification Kit No. AMK 71-10 or any equivalent modification submitted to and approved by the Chief, Engineering and Manufacturing Branch, FAA, Central Region, and thereafter operate the aircraft in accordance with the flight manual revision provided with the kit. NOTE: If polystyrene battery cells are replaced with nylon battery cells, the aircraft need not be modified within 10 hours' but may be operated up to 50 hours' time in service after the effective date of this AD. C) Until Paragraph B is accomplished if any ground operation discloses a weak battery, prior to further flight, check both aircraft batteries in accordance with applicable Learjet Service Manual instructions and make needed battery repairs or replacement and conduct all flight operations in accordance with Learjet Service Bulletin 23/24/25-224 dated April 14, 1971. NOTE: The Service Bulletin was incorrectly cited as 23/24/25-225 in the air mail letter dated July 20, 1971. This amendment becomes effective August 3, 1971, to all persons except those to whom it was made effective by letter dated July 20, 1971.