Boeing D6-81926 Equipment Vibration Test Requirements

Boeing D6-81926 provides vibration-related reference requirements for Boeing engineers responsible for the preparation of equipment Specification Control Drawings (SCD) and for equipment supplier engineers who prepare Qualification Test Procedures (QTP) and Qualification Test Reports (QTR).

Summary of Boeing D6-81926 Equipment Vibration Compliance Testing

The purpose of Boeing D6-81926 is to:

• define consistent equipment vibration and shock qualification design/test requirements for all Boeing commercial airplane models.
• summarize equipment acceleration load factors required by FARs.
• define Fan Blade Failure vibration design/test requirements for flight-critical equipment.

The equipment test requirements defined in Boeing D6-81926 apply to all models of Boeing commercial aircraft. This document is intended for:

• new equipment.
• existing equipment that is being installed in new locations on
• new/derivative aircraft.
• existing equipment that is being modified sufficiently to warrant retesting.

Section 2. Vibration Qualification Requirements

Equipment vibration qualification testing demonstrates if equipment functionality and durability are sufficient to provide trouble-free service over the aircraft design life. To accomplish this in a relatively short test time, the vibration test levels are higher than the actual service vibration environment. The test levels are derived using standard time compression methods based upon a fatigue failure mode. Equipment to be qualified for use in Boeing commercial airplanes can also be tested to the requirements of DO-160.

The vibration test consists of frequency response testing. Next, this is followed by a random vibration endurance test. Testing is generally conducted until all test requirements have been met or a malfunction or failure occurs.

In some cases, the equipment can be qualified for vibration testing by similarity using the previous testing. Equipment can also be qualified by similarity to a part with a successful service history. Similarities are justified by the following:

• Similar equipment items must have a comparable structural dynamic response
• For similarity by testing, the testing must meet or exceed this document’s requirements
• For similarity to service, the equipment must perform similar functions and be mounted in similar airplane locations.

Vibration Qualification Test Procedure

A proposed test plan of the vibration qualification procedures will consist of the following. Note that this list is not all-inclusive.

• The vibration test envelope and test duration
• Quality or conformance inspection
• An identification of the prototype or pre-production equipment items.
• Defined test configurations
• Success and failure criteria

After the completion of the test program, a report is issued with the following information:

• Summary of the testing performed with results and conclusions
• The vibration test log
• Results of the post-vibration performance test
• Photographs of the components showing the teardown and inspection, including areas of wear, fatigue, or failure

Section 3. Shock Qualification Requirements

Shock testing is generally also required when testing to Boeing D6-81926. The purpose of a shock test is to assess equipment integrity under dynamic load conditions. Additionally, shock testing provides a measure of resistance to handling shock damage. Shock damage may ultimately be important in establishing overall reliability.

The test is performed using an electrodynamic shaker. Most tests will apply the shock pulse in both the (+) and (-) directions for a total of 6 shocks.

Numerous shock tests are provided within the Boeing D6-81926 compliance test standard. It is up to the equipment manufacturer and test lab to determine what best suits the equipment’s testing needs.

Bench Handling Shock Test: This test is recommended for all equipment items. Bench handling shock testing evaluates the ability of equipment to withstand shocks encountered during servicing.

Shipping Container Test: The shipping container with the equipment installed is dropped on a flat concrete surface. This is carried out once on each face. The height of the drop is selected from 10 inches to 30 inches depending on the weight of the container with the equipment enclosed. The equipment must not show any failure, malfunction, or out-of-tolerance performance.

Operational Shock Test: This type of test subjects the equipment to dynamic shocks. Operational shock determines if the operation or structural integrity of the equipment is affected. Generally, vibration testing will subject an item of equipment to a more severe dynamic environment than an operational shock test.

Emergency Landing Shock Test: All equipment that operates after an emergency landing is required to withstand a shock pulse. Emergency landing shock testing shows the functionality of the equipment after the application of the shocks.

Bird Strike Shock Test: Though an in-flight bird impact is rarely occurring, impacts affect the forward pressure bulkhead, cockpit windshield, or crown area. The bird strike shock test is expected to be a high g. and high-frequency shock transient which rapidly attenuates as the structural distance from the impact increases.

Section 4. Acceleration Qualification Requirements

The purpose of acceleration testing is to ensure sufficient structural integrity for the airplane operating environment, and in the case of Emergency Landing Loads, to protect passengers and crew in the event of an emergency landing. The purpose of shock testing is to evaluate any susceptibility to damage during bench handling, shipping, emergency landing, and in a few unique cases, the airplane operating environment.

A static pull testing facility is used to demonstrate the structural integrity of the equipment housing and mounting attachments. Electrical-mechanical components that are generally mounted within or on the equipment case may be removed.

This test will not verify that internal components stay attached under acceleration loading. To verify no performance degradation occurs after limit load, a centrifuge test is appropriate. The procedures are listed below.

• First, the equipment is secured using a rigid test fixture and mounting means.
• The applicable limit test load is applied for a minimum of three seconds in each direction of load. The loads may be applied sequentially. At the conclusion of the limit load tests, the test article is inspected. No permanent detrimental deformation or degradation is allowed.
• The equipment is then re-secured to the static load or centrifuge using a rigid test fixture and mounting means intended for the in-service installation.
• Lastly, the test loads are applied for a minimum of three seconds in each direction of load. The loads are applied using a strap or other means such that the resultant load acts through the nominal equipment. Bending or distortion of the equipment is permitted. However, no failure of the mounting attachments is allowed.

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