Landing Gear Maintenance "Best Practices"

by James Careless, Aircraft Maintenance Technology (AMT) Contributor, AMT on-line magazine ( This article originally appeared in the October 2008 issue of AMT Magazine and is reprinted with permission.

Vulnerability here can increase overhaul costs

Landing gear: At first glance, it appears to be the most rugged part of an aircraft. But landing gear's apparent robustness masks its vulnerability to corrosion and stress damage due to impacts-a vulnerability that can result in a substantially reduced operational lifespan (well below manufacturers' specs) and increased overhaul costs.

What can an aircraft technician do to keep landing gear in top condition between scheduled overhauls? According to Goodrich's Landing Gear Division in Burlington,Ont., quite a lot.

Understanding the life of landing gear
The life of an average aircraft's landing gear is a hard one. At all times, its pressurized oleo-pneumatic shock absorbers exert stress on their metal housings. Meanwhile, the force of hitting the runway upon landing stresses the entire system no matter how gentle the landing. Horizontal forces are also exerted on the gear as the aircraft brakes during landing or accelerates during takeoff.

That's not all. Towing strains the forward landing gear, especially if the tow is not executed gracefully. Add impacts and collisions with other objects on the tarmac, and landing gear can be bent, cracked, and even collapsed due to aircraft accidents.

In the hangar, "landing gear can be damaged by inappropriate jacking and other forms of mishandling," says Jay Lind, Goodrich Landing Gear Quality Assurance Manager. "Even pressure washing the gear to make it look spotless can cause problems because it can force water into the bushings and joints, causing corrosion."

If this isn't enough to worry about, certain solvents such as paint stripper can cause "hydrogen embrittlement" in gear. What happens is that atomic hydrogen found in such substances interacts chemically with the high tensile steel in the gear, causing the affected areas to transform chemically into a brittle alloy with a risk of fracturing. "The only way to counteract hydrogen embrittlement is to remove the affected component and bake it in a special oven at 375°F for 23hours," Lind tells AMT. "This allows the hydrogen atoms to migrate to the surface and then escape."

Maintenance best practices
When damaged aircraft landing gear comes into the shop, it costs more to overhaul than landing gear that has been maintained properly. Here is what you can do to keep your landing gear costs down.

The first step is lubrication. It may sound simple, but insufficient lubrication during regular usage causes unnecessary wear-and-tear in many of the system's components.

"Lubrication is critical to the movement of all articulated parts and joints of landing gear," says Lind. "Proper lubrication ensures smooth functioning, less friction and wear, and the appropriate transfer of forces throughout the gear during use. Lubrication is key to keeping out water, de-icing fluid, and other corrosion-causing substances. Make no mistake; corrosion is a real problem for landing gear."

Before you lubricate, be sure to check the aircraft's manual to find out what substances you can and cannot use. "In some cases, using the wrong grease can be as detrimental as insufficient lubrication because it can cause damage to the gear's bushings," says Lind.

Another best practice in maintaining landing gear is protecting it from paint strippers and other corrosive agents. This is due to the interaction between hydrogen and the high tensile steel used in the gear. If acids are allowed to contaminate the gear, the resulting hydrogen embrittlement can lead to cracks. At the least, such cracks are expensive to fix. At the most, the cracks may be sufficiently large that the component has to be scrapped and replaced-hopefully before the gear fails in use.

Avoiding impacts of any kind is one more best practice for landing gear maintenance. The pressurized shock-absorbing struts are particularly vulnerable to nicks, dings, and dents. "Any change in the shape of the struts, or indeed any other support structures of the gear, results in ‘stress risers' in the component," says Lind. "This makes it more vulnerable to failure due to metal fatigue, potentially long before the next scheduled overhaul comes about."

When things do go wrong-and things do-it is important to document the kind of accident suffered by the gear and what visual damage can be seen. The smartest thing to do in such cases is to swap out the component immediately and send it off for nondestructive testing and repair, accompanied by the record of what happened to it. This allows landing gear manufacturing repair organizations (MRO) such as Goodrich to do the repair work accurately before the damage becomes more serious and thus more expensive to fix.

Documentation of each serialized part of your gear is also vital for keeping overhaul costs down. "Like engines, serialized components in landing gear have specified operational lifespans, after which time they must be replaced," says Lind. "In cases where we do not have such information, we have no choice but to scrap the undocumented part and replace it with something new. The same is true for parts with illegible serial numbers. Unless we can be sure of their history and lifespan, we have to scrap them."

Operational conclusions
The landing gear best practices outlined by Lind can be distilled into a series of "operationalconclusions" or fancy words for things you should do as a matter of course to keep your gear at optimal condition.

First things first: For every piece of gear you service, go over the manuals. In particular, compile a list of "forbiddensubstances" that should not be used around unprotected gear. Also double-check the regular maintenance/lubrication protocols because these can differ from aircraft to aircraft.

Next, go over the documentation for the gear you service. Is there a complete history for each serialized component? If not, spot the holes and be prepared to replace the undocumented parts. After you've incurred this expense, keep complete records to avoid having to pay for it again.

Third, review your shop's procedures to ensure that other unrelated work such as paint stripping and cleaning are not putting your gear at risk. Where required, either protect your gear from overspray or change your stripping/cleaning processes.

Fourth, ensure that there is a complete reporting procedure for each aircraft's landing gear, both to alert you to accidents when they happen and to provide accurate historical information for the overhaul shop. This may require a slight change in corporate culture, i.e. to one where reporting a mishap doesn't necessarily lead to disciplinary action. If your staff is scared to report accidents, they won't...and you will pay the price later during overhauls.

Finally, don't be fooled by the apparent robustness of landing gear. Like every other critical system on an aircraft, landing gear has its own vulnerabilities that have to be monitored and cared for-at least if you want to keep overhaul costs down and flight safety up.

Don't Cry "Wolf": How to Reduce the Impact of False ELT Alerts

by Carole Smith, Communications, National Search and Rescue Secretariat (NSS)

All false emergency locator transmitter (ELT) alerts place a burden on Canada's search and rescue system, and most importantly, may divert resources from responding promptly to an actual aircraft in distress. Pilots, air traffic controllers, and flight service specialists who overhear ELT signals on 121.5MHz also take time away from other duties to forward these alerts to rescue authorities.

A few simple rules of thumb can help aircraft owners, operators, and maintainers minimize false ELT alerts. Search and rescue is a shared responsibility, and we can all do our part.

406 MHz ELTs
An ELT operating on a primary frequency of 406MHz sends a half-second digital burst transmission once every 50s. This coded signal is captured by the Cospas-Sarsat satellites, and relayed automatically to search and rescue authorities. The unique code is then cross-referenced with the Canadian Beacon Registry to obtain vital information about the aircraft in distress.

It is important to note that all 406MHz ELTs also transmit a continuous analog homing signal on 121.5MHz. While the 121.5MHz signal is no longer detected by satellite, it is used by search and rescue aircraft and ground crews to travel the final distance to the scene of an accident, particularly when visibility is reduced due to precipitation, terrain, vegetation, or darkness.

The following actions can help minimize false alerts from 406MHz ELTs:

  • Register your 406MHz ELT with the Canadian Beacon Registry System. It's required by the Canadian Aviation Regulations(CARs). Registration is free, and can be completed on-line at; by calling
    1-877-406-SOS1(7671); or by faxing a completed registration form to 1-877-406-FAX8(3298). It is recommended that registration be completed even before installation. If a 406MHz ELT is activated by mistake while being installed, an alert can be more quickly resolved if a point of contact has been registered.
  • Carry out routine operational checks of 406MHz ELTs in strict accordance with the manufacturer's instructions, as each model has its own unique test procedure. Consider building this protocol into your operating checklists, as applicable. The manufacturer's documentation will also indicate how often these checks should be carried out to ensure that the maximum battery life of the unit is preserved.
  • Routine 406MHz ELT tests that involve transmission of the 121.5MHz homing signal should only be carried out during the first 5min of every UTC hour, and for a duration of 5s or less.
  • The digital signal from a 406MHz ELT that is turned on for approximately 50s or more will be captured by the search and rescue satellites, and interpreted as a distress transmission. If you believe this may have happened in error, contact the Canadian Mission Control Centre(CMCC) at 1-800-211-8107. The staff will welcome your call, and there is no fine or charge levied by the search and rescue system for inadvertent activations of this kind.
  • Keep your Canadian Beacon Registry information up to date. If you or your emergency contacts move, or if you buy, sell, or substantially reconfigure your aircraft (e.g. new paint colours, change floats to wheels, etc.), be sure to update your record. If the aircraft is sold, and the 406MHz ELT registration is not updated, the original owner will be called if the ELT is triggered. This confusion could delay a rescue effort. It is also a good idea to update your record when the ELT is removed from the aircraft for re-certification or for extended storage.

121.5 MHz ELTs
As of February 1, 2009, signals from ELTs operating on a primary frequency of 121.5MHz (and/or 243MHz) are no longer captured by search and rescue satellites. However, 121.5MHz is still monitored by air traffic control(ATC) towers and flight service stations(FSS) during their hours of operation, and by some aircraft. ELT signals overheard on 121.5MHz are reported to search and rescue authorities as possible distress transmissions.

The following actions can help minimize false alerts from 121.5MHz ELTs:

  • Test your 121.5MHz ELT only during the first 5min of every UTC hour, and for a duration of 5s or less.
  • Contact your closest joint rescue coordination centre (JRCC) if your 121.5MHz ELT activates by mistake. Include the location, time, and duration of the inadvertent transmission, if known. There is no fine or charge levied by the search and rescue system, and the rescue controller will welcome the opportunity to focus on another case that might involve an actual aircraft in distress.

An important note on ELT disposal
An increasing number of 121.5MHz ELTs are being removed from service as aircraft are fitted with newer 406MHz units. It is very important to ensure that these 121.5MHz units are properly decommissioned, including removing the battery from the unit and disabling the electronics. Several unnecessary searches have concluded at local garbage dumps due to an emergency beacon that had been improperly discarded. Curious children have also activated ELTs and other types of emergency beacons after finding them around the house or workshop.

Canadian Beacon Registry System:
Tel.: 1-877-406-SOS1 (7671)
Fax: 1-877-406-FAX8 (3298)

Canadian Mission Control Centre (CMCC) (Cospas-Sarsat alerts):
CMCC Trenton 1-800-211-8107

Joint Rescue Coordination Centres (JRCC):
JRCC Victoria 1-800-567-5111 (B.C. and Y.T. only) or +1-250-363-2333
JRCC Trenton 1-800-267-7270 (Canada-wide) or +1-613-965-3870
JRCC Halifax 1-800-565-1582 (Eastern Que. and Atlantic Canada only) or

Fatigue Risk Management System for the Canadian Aviation Industry: Employee Training Assessment(TP14574E)

This is the third in a seven-part series highlighting the work of the Fatigue Risk Management System(FRMS) Working Group and the various components of the FRMS toolbox. This article deals with TP14574E, Employee Training Assessment. Intended for use by trainers, this optional module provides an assessment of employee competence in topics covered in the Fatigue Management Strategies for Employees(TP14573E) workbook. We encourage our readers to consult the complete toolbox documentation by visiting -Ed.

The purpose of this assessment is to evaluate individual competence in each of the topics covered in Fatigue Management Strategies for Employees. Each chapter in the workbook begins with a set of learning outcomes that detail the knowledge and skills to be learned by the end of each chapter. Students should have completed each of the exercises and knowledge checks in the workbook before beginning this assessment.

The assessment process uses two approaches to evaluate employee competency in fatigue management. First, employees are asked direct questions intended to assess knowledge obtained from the workbook. Employees are also asked to maintain a logbook to demonstrate competence in applying the concepts of fatigue risk management to their specific work, social, and family situations.

This booklet consists of five elements:

  • Fundamental Knowledge Questions
  • Employee Logbook Instructions
  • Acceptable Responses to Fundamental Knowledge Questions
  • Logbook Checklist
  • Competency Assessment Results

The first two elements form the assessment tasks and should be completed by employees. The Acceptable Responses and the Logbook Checklist are intended primarily for a designated assessor to determine whether employees have provided appropriate answers and information. However, it may be useful to provide this material to employees during the assessment. This will ensure employees know the types of answers/information they are expected to provide for each question. If the answers to the fundamental knowledge questions are provided to employees, the assessor should conduct a verbal assessment, asking questions at random. The assessor should primarily ask the highlighted questions on page 3 of the online document (see link provided below).

The form provided in Competency Assessment Results serves as a certificate of competence. The feedback provided on this form should state whether the individual has demonstrated competence in fatigue risk management and highlight any areas that need further attention.

The assessor may be a safety manager within the organization who has achieved competence in fatigue risk management principles. Alternatively, assessors can be commissioned from external sources (such as universities or private consultants) to provide a more objective examination of employee responses.

How to use this assessment unit
First, ensure the workbook exercises have been completed. These questions can be used to determine how well the topic information has been understood.

Employees should complete the first two parts of the assessment:

  • Fundamental Knowledge Questions; and
  • Employee Logbook Instructions.

The Fundamental Knowledge Questions can be answered in the space provided in this booklet. The logbook should be completed in a separate notebook on a day-to-day basis for one month. Employee Logbook Instructions outline a number of elements that should be demonstrated and/or considered within the actual work environment. Employees should cover each element in their logbooks. If the organization already practises good fatigue risk management principles, and the employee already understands and uses these principles, the logbook can be completed retrospectively. That is, employees can detail how they approached the required elements listed on pages 9–10in their specific work environment in the past.

Assessment criteria
The knowledge questions and the logbook form the majority of the assessment criteria. To complete the course, employees should have a one-on-one interview with a designated assessor. The assessor asks random questions from the Fundamental Knowledge Questions to test the employee's understanding. The assessor also asks questions based on the logbook, calling for the employee to describe how various components of fatigue risk management were applied to the specific work situation. Following the interview, the assessor completes the Competency Assessment Results form on page19 and provides feedback to the employee based on the assessment.

We conclude this overview of TP14574E by encouraging our readers to view the entire document on-line and familiarize themselves with the five elements described above. Go to

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