KLM Royal Dutch Airlines

Comment on NPRM 2012-NE-05-AD There is a difference in compliance date of the SB 3910001-49-A16255 (prior to June 1, 2015) and the Canadian AD (42 months after Nov. 16, 2011 which is May 16, 2015. What will be the compliance date for the FAA AD? AD doesn't reply to the root cause (blade failure). Accomplishment of the expensive SB 3910001-49-A16255 will not prevent costly HPT blade failures from happening. SB 3910001-49-16250 introduced an improved HPT blade; we suggest a later compliance date for APU's modified per SB 3910001-49-16250 as the risk for these blades is lower than the pre-SB blades. Opportunities to perform SB 3910001-49-16255 in the past, before the Canadian AD, were missed because spare parts were not available. Now the operators are forced to modify their whole population in only 42 months. This can not be achieved without forced unscheduled APU replacements. Waiting for an Overhaul is not always possible. According Hamilton Sundstrand the MTBUR of the PW901A APU is 7389 APU hours, this means around 5.8 years. 42 months is only 3.5 years. For this reason a later compliance date is requested. As not all APU's can be modified during an overhaul, extra man hours have to be spent. Costs include extra shop costs and APU replacement costs on an aircraft. This is in contradiction with the statement in the SB; "No more man-hours are necessary to include this service bulletin at overhaul." Furthermore, the weight will increase by 3.05 pounds (1.38 kgs). This also will lead to extra (fuel) costs for the operators. This is not in line with the statement in the NPRM; 3. And will not have a significant economic impact.