What this means is that the FAA has to give you an "Ok" to work on those aircraft, making sure that you have submitted an outline of a program for the maintenance that will be done. This is not needed for part 91 aircraft. This is just one example of how part 135 is much more strict than part 91; many more will be in this paper. This is to be expected, however, due to the fact that under part 135 passengers are being carried for hire, therefore more safety measures must be taken.
Some, however, do not believe that the manufacturer's recommendations may be the best way to do maintenance on certain aircraft. "Recently the FAA has been concerned about the completeness of manufacturer maintenance programs and has been requiring operators to develop AAIP's (approved aircraft inspection programs) as a solution. According to FAA officials, the inadequacy of the manufacturer programs lies in the area of equipment that has been installed since the aircraft was new that the airframe manufacturer does not address. These items should, however, be maintained as per the equipment manufacturer recommendations. One significant problem found in using AAIP's is the separation of such inspection programs from the manufacturer's revision system. Aircraft maintained in accordance with the manufacturer's recommended maintenance program are constantly up to date with new manufacturer recommendations." (Hertzler, 1998). .
So what are the major differences in working part 135 aircraft than on part 91 aircraft? First of all, all service bulletins issued by manufacturers are mandatory under 135; they are advisable but not mandatory under 91. All specific overhaul periods for engines, propellers, and accessories have to be performed under 135; under 91 it is just a suggestion. These time periods are for time in use and for calendar time as well. This also pertains to fluid carrying hoses that need to be replaced on a timed schedule also.