Maintenance and Certification

On Maintenance Errors

The following article by Joe Scoles (JS) was originally published in Issue 4/1998 of Aviation Safety Maintainer and is republished for its enduring value as a safety promotion tool.

The following is a list of eight maintenance errors compiled by Robert Sargent, a maintenance human factors engineer at the Boeing aircraft company. After reading this list, I reviewed the errors that were tabled in Maintainer articles back as far as 1982. As a result of my findings in these articles, I not only agree with Mr. Sargent's list, but I find very few new issues that could be added. Mr. Sargent did an excellent job in his research and he also brings to light the importance of those very simple maintenance items that cause so much trouble. Could it be that shift change and work practice often enter the picture?

  1. Incorrect installation of components;

  2. Electrical wiring discrepancies;

  3. Inadequate lubrication;

  4. Fuel or oil caps and fuel panels not secured;

  5. Fitting of wrong parts;

  6. Loose objects left in aircraft;

  7. Access panels/fairings/cowlings not secured; and

  8. Gear pins not removed before departure.

    I would like to add to this list:

  9. Pitot/static covers and/or tapes not removed after maintenance;

  10. Inadequate inspection or faults missed during inspection; and

  11. Work not in accord with standard or accepted practice. — JS.

Although AMEs are aware of these simple human inadequacies, they still end up getting caught out on a limb occasionally. Let us imagine that typical errors are tied to a chain with a noose on the opposite end, which is looped around the neck. As you read the incident examples below, think about how the outcome might have changed if the noose tightened around the subject's neck every time he or she walked away from an aircraft when simple but important items were missed during inspection and maintenance.

Boeing B737 — The crew declared an emergency and returned for a safe landing after the No. 1 engine failed shortly after takeoff. After landing, the crew shut down the engine and, during taxi, they observed fuel leaking from the engine cowling. Maintenance reported that the engine had spooled down owing to a large fuel leak near the dump valve. Further examination revealed that the leak had occurred because a ferrule was missing from the coupling that secured a high pressure fuel line to the dump valve. Maintenance installed the ferrule, secured the fuel line coupling and returned the aircraft to service.

McDonnell Douglas DC-10 — Shortly after takeoff, passengers reported fuel leaking from an outboard wing fuel panel. After verifying the report, the pilot decided to dump fuel and return to the airport. Maintenance found the source of the fuel leak to be two large screws that had been incorrectly installed in the leading edge of the wing and had punctured the fuel tank. The aircraft had been on lease to a foreign operator when the oversize screws were installed. The correct size screws were installed, the fuel tank was resealed and the aircraft was returned to service.

Cessna A-185F — During cruise flight, the engine (Continental IO-520-D) quit. The pilot was uninjured and the aircraft undamaged during the forced landing on a pond. Inspection of the aircraft revealed that the bolt connecting the throttle cable to the throttle had become dislodged. The report indicated that the cotter pin had failed and the nut had come off. The report did not explain how it was determined that the cotter pin failed.JS.

Cessna 337 — The pilot declared to air traffic control that both engines had failed, then subsequently reported that he had restarted the engines. He landed safely at a nearby airport. Further investigation revealed that both engines were operating from one fuel tank. The gauge for this tank was indicating over half full at the time the engines stopped. An inspection revealed that the fuel tank was empty, and the fuel gauge was reading incorrectly. The one time that a fuel gauge is supposed to be accurate is when the tank is empty.JS.

Cessna 172 — The aircraft departed on a local VFR training flight and, shortly after takeoff, the pilot reported a very rough running engine and returned to the airport, making a safe landing. Maintenance declared there were no discrepancies with the aircraft and it was ground run with no problems. Maintenance suspects that the fuel selector was slightly off the detent for one of the tanks and that this may have interrupted the fuel flow. Maintenance went on to state that there is some "play" in the selector switch and it is possible the selector may have been positioned incorrectly.

From my experience with Cessna aircraft, I do not entirely agree that "play" is part of a correctly functioning and rigged fuel selector. What we seem to be discussing is excessive wear somewhere in the fuel valve control. The inexperienced student may have focussed on the pointer, not realizing the selector could be off the detent.JS.

de Havilland DHC-8-102 — The aircraft diverted to an alternate airport because of a radar failure. Before landing, the crew reported an unusual odour in the cockpit, which may have indicated an electrical problem. Company maintenance discovered a shorted out No. 1 advisory display panel. The advisory display panel was replaced, the system checked and the aircraft returned to service.

This raises a broader issue: did the circuit protection devices work as advertised or did the advisory display panel simply burn itself off-line? This point was not discussed in the incident report, but it is important to keep in mind whether electrical systems always function as required to cut off the flow of current when a short occurs. — JS.

I'll close with a couple of cases that reflect the old classic involving items pilots often miss during pre-flight. Maintenance people can help pilots prevent such incidents through awareness and vigilance.

Cessna 421 — The aircraft departed Thompson, Man., on a medical transportation flight with two pilots and a flight nurse on board. Shortly after departure, the pilots noticed oil on the cowlings of the left engine. They shut it down, declared an emergency and returned to Thompson. Examination of the aircraft indicated that the oil had come from the engine oil filler, whose cap had been left unsecured after the pilots' pre-flight check.

Cessna 310 — The aircraft departed Sioux Lookout, Ont., but declared a Mayday and returned shortly thereafter owing to an open exit door. Inspection after landing revealed that the door was not properly secured before departure.

FAAST Tips on Maintenance—Older General Aviation Aircraft

The Federal Aviation Administration (FAA) Safety Team (FAASTeam) publishes a very useful series of monthly maintenance tips. They include references to the FAA and other American associations such as the AOPA, EAA, etc. Given that the fabric of our own Canadian general aviation (GA) industry is inextricably tied to the American GA system and manufacturers, the tips are universal and are applicable to Canadian aircraft. Tips are not regulations or directives but serve a purpose of outreach, education and awareness. If you have any questions on the material presented below, feel free to contact us. The FAASTeam’s online maintenance tips are republished with their generous permission.

Aging Aircraft in General Aviation (GA)—Best Practices

Part 1: Introduction

How often do you work on old or aging aircraft still in operation? Unfortunately, manufacturers of those aircraft may have gone out of business, and those that still exist might not be able to provide field support. Engineering drawings, maintenance procedures and technical data other than the FAA’s Advisory Circular 43-13 (AC43-13) just aren’t available from nonexistent manufacturers.

Before you work on that old aircraft, ask the owner for all the acquired, organized or preserved data about their aircraft. Reviewing this data greatly increases the likelihood of improvements in maintenance practices and safe operation of a particular aircraft. These actions can have an enormous impact on the continued airworthiness of an aging aircraft when you approve it for return to service.

Next, we will talk about two specific best practices that can have a fundamental impact on your approach to maintenance and inspection of aging aircraft. These are records research and special attention inspections relating to aging aircraft. Doing either of these helps assess the condition of an aircraft. You need both to thoroughly assess the effects of aging (corrosion, metal fatigue, inspection techniques, wiring deterioration, etc.) on an aircraft and monitor its condition during future operations.

Part 2: Records Research

What is your first step in determining the condition of an aging aircraft? It should be records research! The records will help you determine the degree of inspection necessary, as well as what items may have already been inspected. Your research will help to identify a particular aircraft’s maintenance and usage characteristics as well as the areas of an aircraft model type or class that may require closer attention.

Inspection and overhaul recommendations contained in older GA aircraft maintenance instructions may not provide adequate guidance regarding aging issues. Therefore, assessing the quality of maintenance and inspections during an aircraft’s life is important to determine which parts have been replaced, if corrosion was ever a problem and other maintenance factors that could lead to a concern with aging.

If you are going to work on an older aircraft, ask the owner for all available information so you can establish the maintenance history. Your knowledge and experience will help to reveal if there are voids or missing information. Advise the owner about these discrepancies and offer to help get the information.

You can compare research about more general model type issues with individual aircraft information to identify similarities and differences. In effect, this helps answer the question: Does the information I am seeing on this particular aircraft match the history of the aircraft records?

Once collected, the information will help you and the owner establish a baseline to determine what maintenance, repairs and alterations have been done and how well the aircraft has been cared for.

Part 3: Special Attention Inspections

Your assessment of an aircraft’s paperwork is only the prelude to a thorough aging evaluation. For aging aircraft, the normal annual inspection minimum requirements specified in 14 CFR 43.15 Appendix D or those recommended by the manufacturer may not be enough. You may need to do a detailed inspection, a series of inspections, modifications, part replacements or a combination of these actions to maintain airworthiness and keep an aging aircraft operating safely.

As an aircraft ages, the inspection methods and techniques may change from what was previously required. High aircraft time, severe operating environments, inactivity, outside storage, modifications or poor maintenance can all prompt a special inspection. The records research will provide information for owners and mechanics to discover what a particular aircraft or aircraft type may need.

Special inspection criteria can be written to pertain to a specific aircraft or aircraft type. In the reference listed below, you will find an “Aging Airplane Inspection and Maintenance Baseline Checklist”. You can use this checklist as a starting point to develop a model- or airplane-specific inspection and maintenance checklist.

The design concepts of systems (mechanical, electrical and flight controls) and structures (layout and materials) are similar from model to model and from manufacturer to manufacturer for most aging GA aircraft. Areas typically susceptible to aging have been identified.

This concludes the GA aging aircraft series of maintenance safety tips. This should also be where you begin to modify or enhance your maintenance techniques when working on aging aircraft. We highly recommend you review the publication titled “Best Practices Guide for Maintaining Aging General Aviation Airplanes”, which can be found at:

Share the guide with your maintenance colleagues and pilot acquaintances that work on and/or fly these older aircraft.

New Advisory Circular: Segmented Passenger Weights for Part 703 Operators

Did you know that….

…with the coming into effect of Subsection 723.37(3) of the Commercial Air Service Standards (CASS) on July 30, 2012, weight and balance calculations for aeroplanes operating under Subpart 703 of the CARs can no longer use the standard passenger weights published in section RAC 3.5 of the Transport Canada  Aeronautical Information Manual (TC AIM)?  The amended standard calls for operators of aeroplanes under Subpart 703 of the CARs to determine the weight of passengers by using either actual weights or segmented weights (TCCA published or air operator derived), as described in Advisory Circular (AC) No. 703-004, titled “Use of Segmented Passenger Weights by Commercial Air Operators under Subpart 703 of the Canadian Aviation Regulations”. For complete details, please consult the AC 703-004 linked above as well as section RAC 3.5 of the TC AIM.

Date modified: