Parts: The lifeblood of aviation

Most gyroscopic equipment does contain internal cages or stabilizing mechanisms to secure the internal moving parts during periods of inactivity. In the event that physical damage is noticed on a shipping container used for inertial equipment it is worthwhile to return the device to an agency for a complete operational assessment prior to installation in an aircraft. It is a common practice to see force sensors included in shipping boxes involving motion sensitive components. These often consist of a delicate glass tube containing a colored fluid, all encased within a small sealed box with a viewing window. In the event of a significant mechanical jarring, the inner glass tube will shatter and release the colored fluid within the box. When the viewing window is checked by the person receiving the part, the colored fluid is observed. This should be a cause for rejecting the component and possibly filing a claim with the shipping agent. Other types of mechanical “G” force sensors are frequently used as well.

The use of shock detectors is not always a standard practice. There are vendors that require specific instructions from the customer to include these telltale devices in parts shipments. Taking into account that gyros and inertial sensors are not always easily accessible once installed, having pre-emptive knowledge that the unit may have been exposed to a damaging circumstance may offset an inflight failure or a mission canceling fault.

Flight deck and cabin displays may also require special attention when shipping is required. Most new technology display monitors are required to meet stringent impact criteria and will frequently survive even the most aggressive delivery person.

One recent event involved a liquid crystal display (LCD) monitor that remained overnight in a nonheated environment with sub-zero outside temperatures. When the technician received the device in the morning and installed it in the aircraft, it would not initially come up when power was applied. After several moments the technician shutdown the aircraft and assumed the received unit was faulty and went to order a replacement. In the mean time, another technician turned on power and within a short time the temperamental display began to operate. This feat did not involve sacrifice or incantations. In fact, the display contained an internal heating network and a temperature sensitive switch that would prevent the device from working until the internal temperature reached 50 F. This bit of information was not readily available at the time, so the technician replaced the suspect faulty display and received an invoice for testing and re-certification of the part from the airframe manufacturer who returned it to service “no fault found.”

No fault found
The above mentioned phrase “no fault found” is the scourge of many technicians when evaluating a replacement part for installation. Component testing for return to service is usually defined by manufacturers and is accomplished in a controlled environment.

Actual operation within the aircraft will present conditions possibly involving temperature extremes, vibrations, and the result of drastic pressure change. When replacing any aircraft component with one that had been either repaired or overhauled, it is worthwhile to investigate the device’s history. In some cases a part may have been returned to the vendor in the past more than once for repair of a specific defect and is deemed serviceable by the repair agent without finding any failures, only for it to have the same anomaly when installed in the next aircraft.

Many technicians who have been bitten by the words “no fault found” will refuse to install these suspect devices. One particular airframe manufacturer reports approximately 60 percent of its warranty parts have been returned to the field “no fault found.” A situation like this may not always mean the repair agent is not doing their job, but could be an indicator the technicians replacing these components do not really have a good understanding of the systems involved.

Customer support
Honeywell has recently introduced a “Three Strikes, You’re Out” policy on certain repaired components. This effective customer support initiative has repair technicians taking into account some of the nonstandard situations that result in intermittent operation. In the event a covered part is returned for repair three consecutive times for a similar fault, it is subsequently removed from service. In any case, it is the job of the technician to provide the component repair agent with details of the fault. Most of us have encountered flight crews that create a write-up that reads “Inop.” Please don’t do the same thing to our allies in the repair centers.

Reputable parts suppliers who understand the nature of our business are a tremendous asset. This is especially true when you have one located in your area willing to meet you at odd hours to deliver an essential component. (Thank you, Al Zito.)