The FAA’s concern that a critical part on the Bombardier Learjet 45 “was not manufactured per the type design data” led it to ground the entire fleet of 173 U.S. Learjet 45s on August 13. The UK followed suit and promptly grounded the 11 Learjet 45s on that country’s register.

Airworthiness Directive 2003-16-19 appeared in the Federal Register the same day and gave owners three days to make a single flight to the maintenance facility of their choice. Those who were unable to comply were forced to seek a ferry permit after the August 16 deadline. It was not known at press time if any owners had had to resort to this tactic.

The situation stems from an incident last March when an Australian Learjet 45 experienced a severe in-flight vibration accompanied by a dramatic nose-down pitch. The crew was able to recover and land the aircraft without further incident. The FAA initiated an investigation that discovered a broken jackscrew in the horizontal stabilizer actuator assembly (HSAA). On April 11 the FAA issued an AD ordering that existing HSAAs with part number 6627401000-001 be replaced with a new or serviceable HSAA having P/N 6627401000-005.

According to the AD, “The cause of the incident is attributed to brittle fracture material properties of certain components of the HSAA. The requirements of the AD are intended to prevent structural failure of the HSAA, which could result in possible loss of control of the airplane.” The fix was essentially the replacement of the jackscrew. According to those familiar with the fix, the old screw had a small notch in the end, and the crack apparently radiated from that notch. P/N -005 was designed without the notch.

A Bombardier Learjet spokesman told AIN that some operators, hearing of the problem before issuance of the April AD, had the assembly inspected and the part replaced on their own. For its part, Bombardier immediately began putting P/N -005 in all aircraft still at the factory. “After the April AD was issued, there were still about 115 operators who needed the upgrade so they sent their old HSAA to us, we inspected it and replaced the screw with P/N -005, then returned it,” the spokesman told AIN. “We thought that process would take a few weeks but it turned out to be more efficient. It required only seven to 10 days to take care of them all.”

For most, that was the end of the story. No one was hurt, no damage occurred, the entire fleet was upgraded and there were no further incidents–until August 13 anyway. According to AD 2003-16-19, “Although the HSAA having P/N -005 is an improvement over P/N -001, it was not manufactured per the type design data. A brittle fracture could occur on the acme screw and nut within the assembly having P/N -005, similar to that on the assembly having P/N -001. During our investigation of this problem, we determined that the configuration and quality controls over the production of these parts were so deficient that we do not have confidence that the airplane can be operated safely for any period of time. Therefore, this AD allows operation only for the purpose of positioning the airplane where the replacement required by this AD can be accomplished.”

It is worth noting that P/N -005 was manufactured by MPC Products of Skokie, Ill., not Bombardier. Despite repeated calls and e-mails to MPC Products, no one from the company would speak to AIN about the situation. However, Bombardier has expressed strong support for the supplier and P/N -005.

The Learjet spokesman said, “Apparently the FAA didn’t have enough confidence in the quality control of the part itself, but we believe the replacement part addressed the primary cause of the actuator failure. We’ve been doing additional tests that reinforce our position that we’ve done what’s necessary to prevent further failures.”

Since the Australian incident, Bombardier has been actively supporting the FAA investigation. “The FAA feels that subsequent to certification of the part, [MPC Products] made some additional design and build process changes to the -005 unit that did not comply with CFR 21.165(b),” the Learjet spokesman said. “Here at Bombardier, we’ve reviewed those changes and determined they do not compromise the actuator. We’re actively engaged in the FAA process to certify those changes. Bombardier and the FAA have agreed upon a detailed certification plan that will provide the FAA with formal evidence that the actuator, as designed and built, meets all the certification requirements.”

According to an FAA spokesman, there are 230 Learjet 45s in service worldwide, of which 173 are registered in the U.S. He said the largest operator of the aircraft is Flexjet, with a total of 30. ConAgra Foods has a fleet of nine and FedEx Leasing has six. Gold Air International, Southern Company Services and Eaton each have five Learjet 45s, Singapore Flying has four and the remaining aircraft are individually owned by various corporations. Upon issuance of the FAA AD, the UK Civil Aviation Authority fell into step and grounded the approximately 11 aircraft registered in that country.

Plan B

The Learjet spokesman said, “We’re anticipating a 10- to 15-day period to get a firm determination. However, even if the FAA agrees with us on P/N -005, it will probably still insist on an inspection. On the other hand, if it doesn’t want simply an inspection it could well require that we replace P/N -005 with a new part that’s not certified yet. In either case, these aircraft need to be positioned at maintenance facilities to complete the process. Owners should know that we are simultaneously working on the certification of a new part, so regardless this issue should be resolved within the next few weeks. We don’t believe the cost of the fix will be so significant that it won’t be absorbed through the course of our normal business.”

In the interim, there are a lot of Learjet 45s sitting on the ground. Bombardier issued a letter and advisory wire to owners saying it will provide a lift subsidy through Skyjet. According to the Learjet spokesman, the company will provide a subsidy for up to 10 hours a week, with a maximum allowable rate of $2,800 per hour. In the first week, Bombardier will cover 25 percent of allowable costs. For instance, if a company flew 10 hours at $2,800 per hour, Bombardier would reimburse it $7,000. The second week the reimbursement program bumps up to 30 percent and the third and fourth weeks up to 50 percent of the maximum allowable rate.

Subsequent to the recent AD, concerns regarding the Learjet 40 and Learjet 60 have been raised. According to Learjet, the Learjet 40 uses the same actuator but since there have yet to be any aircraft delivered all units will be taken care of at the factory before they are handed over to customers. A Learjet field service representative verified that the Learjet 60 “does not use the same system and is not affected in any way.”