Landing Gear Repair: Information Requirements for Assistance

Operators and repair stations that fix landing gear on Douglas-designed commercial airplanes often propose a repair procedure and request the manufacturer's approval. In addition, they often ask Boeing to provide a procedure not contained in applicable maintenance and overhaul manuals. In either situation, the first step toward receiving a timely response from Boeing technicians is effective communication from the field. Operators and repair stations can greatly expedite the response process by providing pertinent, precise, and complete information about landing gear damage.

Some of the most important information Boeing requires can be categorized by the following subjects:

1 Response time.
2 Problem description.
3 Historical data.
4 Operator preferences.
5 Component dimensions.
6 Preferred method of submitting info.

How rapidly the operator or repair station can expect a response from Boeing depends on the urgency of the repair. If the request for information is generated by an airplane-on-ground (AOG) condition -- a delay in revenue service caused by an unanticipated need for a repair -- operators may expect a response time of one working day. Operators with a non-AOG condition may request an urgent response time of two working days if they can justify an accelerated response.

When requesting repair procedure information from Boeing, the operator or repair station should indicate the specific problem experienced and whether the part in question has been repaired previously. Boeing may require some or all of the following:

Boeing has identified a number of high-stress landing gear components, called safe-life parts, and limited their service life to ensure safe operation. A document approved by the U.S. Federal Aviation Administration (FAA), applicable to each Douglas model, lists all safe-life parts and allowable service lives. Certain information about the airplane is extremely important because it helps determine allowable service lives. This information includes airplane model number, series number, fuselage number, airplane serial number, flight hours, number of landings, and maximum gross weight (MGW).

The request for airplane model and series is particularly important for the repair of landing gear components. Most twinjet landing gear components on Douglas airplanes can be used on several different series of airplanes, each with different loading conditions and MGW. As a result, landing gear components with the same part number can have different allowable repair dimensions and safe-life limits, depending on the airplane series on which it is used.

An example of the effect of airplane series on safe-life limits is illustrated in Table 1. The data show that rework dimensions for the nose landing gear cylinder are unacceptable for DC-9 series 32F, 33, and 41. However, the same repair constitutes a safe-life-limited part for MD-80 series 83, 87, and 88, and imposes no safe-life limits for DC-9 series 21, 32, 34, 34F, 51, and MD-80 series 81 and 82. Reduced cylinder inside and outside dimensions that result from rework affect safe-life limits. This effect varies among different models.

In addition, landing gear parts with no remaining safe life on some Douglas airplane series may be used on another series. Boeing must evaluate these parts before they can be used further. The analysts who evaluate these parts require a complete history of the service of the part on any other airplane.

When proposing a repair procedure, operators should state the repair material type, heat treatment, dimensions, and sizes (including those that are oversize). Giving Boeing additional technical information about any non-standard parts, fasteners, or material reduces the response time requested.

If operators want to make a temporary repair, they must tell Boeing the number of flight hours anticipated until the permanent repair will be accomplished and the proposed date of the permanent repair. Operators that want to obtain FAA approval for a proposed repair must provide the serial number, part numbers, dash numbers, next assembly, service bulletin numbers, and cause of damage.

Repair requests should include all component dimensions pertinent to the repair area. For example, a repair request for the nose landing gear cylinder assembly described in Table 1 should include both the inside and outside diameters, even if only one diameter is reworked. Boeing analysts must assume maximum rework dimension for any dimensions that are not provided. If erroneous, this assumption can result in overly stringent rework limits or even cause a useable part to be scrapped.

Operators should contact their local Field Service representatives or appropriate in-service support organizations to communicate the necessary repair information to Boeing. All repair requests submitted should include correspondence identification that contains a cross-reference to sketch identification numbers.

Operators and repair stations that request assistance from Boeing with landing gear repair procedures can expect to receive a response significantly sooner by communicating all the required information. Particularly important information includes response time, problem description, historical data, operator preferences, and component dimensions.


Remaining safe-life limit (in cycles) for approved inside- & outside-diameter reworks

A number of landing gear components are usable on different series of airplane. The service life and allowable reworks for these components vary according to the airplane series on which it is installed.

Twin-Jet Nose Landing Gear Cylinder Assembly, Part Number 5920602
Thrust Bearing Blueprint Outside Diameter: 4.0490-4.0500 Inches (Before Plating)
Cylinder Blueprint Inside Diameter: 3.3670-3.7000 Inches

Rework Item 1 2 3 4 5
rework O.D. 4.035 4.0395 4.0445 4.046 4.0475
DC-9-21/I.D. 3.71 3.708 3.709 3.71 3.709
0 unlimited unlimited unlimited unlimited
DC-9-33/(C9B) 0 0 0 0 unlimited
0 0 0 0 unlimited
DC-9-34F 0 62,000 unlimited unlimited unlimited
0 161,000 unlimited unlimited unlimited
0 52,000 290,000 unlimited unlimited
MD-88 0 15,000 28,000 30,440 38,000
MD-87 0 38,000 94,000 98,000 unlimited
Notes:"0" means no remaining service life."unlimited" means the cylinder has a safe-life of more than 20,000 landings for the DC-9 and 300,000 landings for the MD-80. It also means that the life of an adequately inspected and maintained structure will not be limited by fatigue problems.

Ron Cambare
Senior Engineer Specialist

Tid Nimitsilpa
Principal Engineer Specialist

Customer Technical Engineering
Douglas Products Division

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