Lucas Grotto

U.S. Department of Transportation Docket Operations, M-30 West Building Ground Floor, Room W12-140 1200 New Jersey Avenue, SE. Washington, DC 20590 Subject: Docket No. FAA-2009-0495; Directorate Identifier 2009-NM-049-AD After review of the NPRM [Docket No. FAA-2009-0495; Directorate Identifier 2009- NM-049-AD] in reference to Learjet Model 60 Airplanes, I have the following comments: It is stated that this proposed AD results from a report of the main landing gear tires blowing out during a takeoff roll and that the AD is being proposed to prevent tire failure, which could result in failures of the braking and thrust reverser systems. It is also stated that in a critical phase of operation such as takeoff, loss of airplane control may result. The NPRM Discussion section speaks of a report of all four of the main landing gear tires blowing out during a takeoff roll of a Learjet Model 60 airplane. The discussion section further states that an investigation of the tire fragments indicates that, in all four tires, there was evidence of internal heat damage consistent with under-inflation, over-loading, or a combination of both. It is stated that tires that have been rolled or taxied at lower- than-specified tire pressure settings may fail. In response to the reason for this NPRM, it is impossible for the general public to comment completely in the time allotted due to the fact that a final report listing all of the findings and any recommendations with supporting reasons for the accident referenced above has not been made public. Any comment made herein is only speculation and may or may not be relevant for why there was an accident involving the blowout of all four main landing gear tires during takeoff roll. I respectfully ask that the comment period be extended to end 45 days following the release of the NTSB Final Report for the accident involving N999LJ so that all of the information that has been determined to be contributing and also to be the cause for this NPRM is made available to the general public and therefore, comments can be made with the data being available to all parties involved. In regards to this NPRM as currently written, I have the following comments: The Costs of Compliance section has been grossly under estimated. The costs listed only cover one event per aircraft and do not take into consideration the recurring action that will be required. Each event at a minimum will be required every 10 days and at maximum every 4 days. Using the average labor rate and time allotted in the NPRM, this calculates out as follows: - Event every 10 days: $2920.00 per product ANNUALLY / $700,800.00 to U.S. Operators ANNUALLY. - Event every 4 days: $7300.00 per product ANNUALLY / $1,752.000 to U.S. Operators ANNUALLY. The estimated cost listed in this proposed AD to U.S. Operators is only 2.8% of what the actual minimum number is and 1.1% of what the actual maximum number is per year and does not take into consideration the indefinite life of the aircraft. Learjet 60 TFMC 2009-03 contradicts Learjet 60 maintenance manual Temporary Revision 12-16 in the following manner: - TFMC 2009-03 states under the note “Aircraft parked for extended periods (10 or more consecutive days) WILL have tire pressure checked periodically in accordance with Chapter 12 of the Learjet 60 Maintenance Manual.” Learjet 60 maintenance manual TR 12-16 Section 1 paragraph A(2) Note states “If the aircraft is parked for 10 or more consecutive days, the tire pressures SHOULD be checked every 10 days while the aircraft remains parked.” It is unclear if the proposed AD requires that you check the pressures every 10 days and this should be clarified. The proposed AD should also state if there are any additional record keeping requirements (as stated in other Airworthiness Directives) in addition to those required by FAR 43.9. It is confusing that the proposed AD requires you to operate the airplane according to the limitations and procedures in TFMC 2009-03, which in turn references you to Chapter 12 of the Learjet 60 Maintenance Manual (TR 12-16), which in turn states that “the date and time of each pressure check must be documented (aircraft logbook entry not required).” The statement “(aircraft logbook entry not required)” in TR 12-16 contradicts FAR 43.9. FAR 43.9 also does not require that you write the time of completion of the work performed, only the date. FAR 43.9 also does not require the documentation of tire pressures as recommended in Figure 301 of TR 12-16 ‘Example of a Tire Pressure Check Record,’ FAR 43.9 only requires a description of the work performed, not the result. Paragraph (a)(4) of FAR 43.9 constitutes that the work was satisfactory, which would include that the tire pressures were within applicable limits at the time of completion of the work performed. In Learjet 60 Temporary Revision (TR) 12-16 Section 1 (Servicing Tires) paragraph A (General), it is stated that the date and time of each pressure check must be documented (aircraft logbook entry not required), however, FAR 43.9 is the governing rule for the content, form, and disposition of maintenance, preventive maintenance, rebuilding, and alteration records (except inspections performed in accordance with part 91, part 125, 135.411(a)(1) and 135.419). FAR 43.9 does not require that the time be documented, only the date. In closing, since the cause of the accident referenced in the proposed AD has not publicly been made available, it can be speculated that the cause of the accident referenced in this NPRM was not the tires blowing out, but that the tires blowing out were a contributing factor to the accident. It can be speculated that the tires were improperly under serviced when last checked due to paragraph 1.A.(3) on page 1 of TR 12-16, which states “Do not decrease the pressure of a hot tire.” This statement is not found in any previous revision of the Learjet 60 maintenance manual 12-10-05 under 1. Service Tires, A. General. The Note remains in TR 12- 16 “Let the tires cool for at least 2 hours before you measure the tire pressure. The pressure indications can be incorrect if measured before the tires have cooled,” as is written in the section of the maintenance manual that TR 12-16 revises. It could also be speculated that the tires lost pressure suddenly due to debris contacted on the runway, which in turn would cause internal heat damage consistent with under-inflation, over-loading, or a combination of both. This proposed AD is unnecessary and financially overburdening on U.S. Operators, and could in itself cause another accident as currently written. To support this statement, I have the following comments: - This proposed AD is unnecessary because it is my belief that the reason for the tires to have blown out on takeoff could potentially be traced back to improperly serviced tires. I speculate that the recommended procedure for checking the tire pressures was not followed during the time it was last checked, and it resulted in the under inflation of the main landing gear tires on the accident aircraft. Also, as a contributing factor to the tires blowing out or as a stand-alone cause for tire failure, it is unknown if the tires on the accident aircraft had ever been, or were currently being operated over-loaded. Each of these conditions, or a combination of both will cause internal heat damage to a tire and is listed as evident on the tire fragments of the accident aircraft per this NPRM. It is also possible that the tires contacted debris on the runway and caused a sudden release of pressure. This could also cause the internal heat damage evident on the tire fragments. Note: These statements are speculative and made based on the fact that the NTSB has not released the final report and probable cause for the accident aircraft. - This proposed AD is financially overburdening on U.S. Operators and will result in significant negative economic impact to each and every U.S. Operator of this product. It is believed that this will have a significant economic impact on a substantial number of small entities under the criteria of the Regulatory Flexibility Act. These statements are substantiated by the gross under estimation of costs per operator in the Costs of Compliance section of this NPRM. As described earlier in this comment, the Cost of Compliance listed in this proposed AD is only 2.8% (minimum) and 1.1% (maximum) of what actual costs will be without taking into consideration that this is an annual, recurring cost. - This proposed AD could in itself cause another accident as currently written. To substantiate this statement, I have the following scenario that could very easily happen. As mechanics, you are strenuously instructed to use the manufacturer’s CURRENT maintenance manual. The proposed AD states in Note 1 “The actions required by paragraph (g) of this AD may be done by inserting a copy of Learjet 60 TR 12-16, dated March 18, 2009, into the Learjet 60 MM. When Learjet 60 TR 12-16 has been included in general revisions of the Learjet 60 MM, the general revisions may be inserted in the MM, provided the relevant information in the general revision is identical to that in the TR.” Should a revision be written that is not identical to that in the TR, and that revision is inserted into the MM, it is possible for a mechanic to use the manufacturer’s CURRENT maintenance manual and follow a procedure that is not meeting the intent of the AD, which could cause an accident. The mechanic may be unfamiliar with the Learjet 60 aircraft and not know that there is an AD written which specifically references material contained in a specific temporary revision that takes priority over the content in a revised, current, maintenance manual. This mechanic, or any person performing preventive maintenance, would now have possible enforcement action taken against them. One might argue that there would never be an instance where the maintenance manual would be revised contrary to this proposed AD, but in retort, I say to that person that the FAA sees it as a possibility due to their statement “provided the relevant information in the general revision is identical to that in the TR” which is contained in this proposed AD. Improper servicing of tires is a danger to any aircraft certified in any category made by any manufacturer. The Learjet 60 aircraft should not be discriminated against. Any Airworthiness Directive written with reference to tire servicing procedures should be written to include all certified aircraft. Aircraft accidents with a probable cause relating to failure of tires that may have been under inflated (improperly serviced) or overloaded during the take off roll have occurred in the past, yet no Airworthiness Directive was written regarding that. To substantiate that statement, refer to the accident of Continental Airlines McDonnell-Douglas DC-10, operating as Flight 603. It overran the runway at LAX on March 1, 1978 when two tires failed, nearly simultaneously, leading to a RTO just prior to reaching V1. The left main landing gear collapsed, which led to a fuel leak and fire, which consumed the left side of the aircraft. The NTSB Aircraft Accident Report AAR-79-1 lists in its findings under Section 3.1 item 13 that the tires on the aircraft may have been operated in the over-deflected condition, since the average inflation pressure was less than optimum pressure for maximum gross weight. The probable cause was determined to be sequential failure of two tires on the left main landing gear and the resultant failure of another tire on the same landing gear at a critical time during the takeoff roll. In place of mandating tire pressure checking procedures for one specific aircraft model, I propose that the FAA develop educational material and awareness of how critical it is to properly maintain aircraft wheels and tires. This could be accomplished in a manner similar to Runway Incursion awareness and educational pamphlets. This would, in turn have a greater benefit to the aviation community because it would raise awareness for all aircraft types affected by this common issue. In my experience, this has been a largely overlooked safety issue in all aircraft. You rarely here of wheel and tire issues causing accidents or incidents, so it is natural for one to become complacent when working in this area. The truth is that proper wheel and tire maintenance and preventive maintenance is very critical and most people follow the recommended procedures, but it only takes one instance for an accident chain to develop. Unfortunately, the chain was not broken in the case referenced in this proposed AD. I appreciate the time you have taken to read my comments. Sincerely, Lucas Grotto Chief of Maintenance Aviation Properties, Inc. P.O. Box 208 Sugar Grove, IL 60554