NTSB Safety Alert SA-022 - Mechanics Manage Risks to Ensure Safety

Mechanics: Manage Risks to Ensure Safety

Carefully f ollow maintenance and inspection

procedures to help prevent aircraft accidents

The problem

 Mistakes made while performing aircraft maintenance and inspection procedures

have led to in-flight emergencies and fatal accidents.

 System or component failures are among the most common defining events for fatal

accidents across various sectors of general aviation (GA).1

Related accidents

Sadly, the circumstances of each new accident are often remarkably similar to those of

previous accidents . This suggests that some mechanics are not taking advantage of the

lessons learned from such tragedies that could help them avoid making the same mistakes .

The following accident summaries2 illustrate some common —and preventable —

maintenance -related accident scenarios :

 A commercial pilot was killed when his Beech 36 airplane struck a tree and the

ground during an emergency landing in night instrument meteorological conditions

following a loss of engine power in flight . The investigation found that the engine had

been reassembled incorrectly during a recent overhaul. Maintenance personnel had

applied silk thr ead and gasket -making material to the sealing surfaces of the main

bearing bosses , which is inconsistent with the engine manufacturer’s maintenance

1 Each year, the NTSB investigates about 1,500 GA accidents in which about 475 people are killed . See the

NTSB data for Review of U.S. Civil Aviation Accidents, Calendar Year 2011 . The defining events information is

derived from the NTSB’s Review of U.S. Civil Aviation Accidents, 2007 – 2009 . Both data sources are

available from the NTSB’s Aviation Statistics web page at

http://www.ntsb.gov/investigations/data/Pages/aviation_stats.aspx .

2 The accident repo rts for each accident referenced in this safety alert are accessible by NTSB accident

number from the NTSB’s Aviation Accident Database & Synopses web page at

http://www.ntsb.gov/_layouts/ntsb.aviation/index.aspx . (The accident numbers are ERA09FA093 ,

WPR10LA284 , and DEN08FA058 , respectively .) Each accident’s public docket is accessible from the NTSB’s

Docket Management System web page at http://www.ntsb.gov/investigations/SitePages/dms.aspx .

SA-022 March 2013 , revised December 2015

instructions . The improper sealing of the crankcase prevented adequate clamping at

the main bearing bosses , which resulted in the fragmentation of a main bearing and

the failure of the crankshaft .

 A private pilot and an instructor were injured (one seriously) during a forced landing

of a Piper PA -46-310P airplane following a loss of engine power during cruise fl ight.

The induction elbow for the Nos. 1, 3, and 5 cylinders was displaced from the throttle

and metering assembly where the elbow couples with the assembly by an induction

hose and clamp. The investigation found that the securing clamp was not properly

positioned per the manufacturer’s instructions, which allowed the induction tube

elbow to separate from the assembly in flight. The induction system had been

recently removed during maintenance .

 An airline transport pilot was killed during a positioning flight after the Piper

PA-23-250 airplane he was flying entered an uncontrolled descent to the ground

following an in -flight separation of the stabilator trim pushrod. The investigation found

that the nut that secured the pushrod to th e trim tab had backed out during flight;

neither the nut nor its cotter pin w as located. Although the airplane had undergone an

inspection about 73 flight hours before the accident, the investigation found evidence

of prolonged inadequate maintenance . This evidence included an elongated attach

hole for the left stabilator trim bellcrank , which allowed for significant freeplay , and

extensive aft streaking along the forward rivet line of both stabilators , which is

indicative of loose, vibrating rivets.

What can maintenance technicians do?

 Remember that well -meaning, motivated, experienced technicians can make

mistakes. Learning about and adhering to sound risk management practices can help

prevent common errors that can lead to tragic consequences .

 Understand the safety hazards associated with human fatigue and strive to eliminate

fatigue contributors in your life. Fatigue has been linked to forgetfulness, poor

decision making, reduced vigilance, and other factors that can interfere with your

ability to do your job safely .

 Pay particular attention to the safety and security of the items that undergo

maintenance and any surrounding components that may have been disconnected or

loosened (possibly to ease access) during that maintenance .

 Carefully follow manufacturers ’ instructions to ensure that the work is completed as

specified. Always refer to up -to-date instructions and manuals when performing a

task, and ask questions of another qualified person if something is unfamiliar to you.

 Have a qualified per son, other than the person who performed the maintenance,

inspect the safety and security of critical items that have received maintenance.

 Be thorough when performing routine inspections. Ensure that items needing

immediate attention are addressed rather than deferred .

SA-022 March 2013 , revised December 2015

Interested in more information ?

Education and training are critical to improving GA safe ty. The Federal Aviation

Administration (FAA) Safety Team (FAASTeam ) provides access to online training courses ,

seminars , and webinars as part of the FAA’s “William (Bill) O’Brien Aviation Maintenance

Technician Awards Program,” which provides mechanics with recurrent training that focuses

on accident and incident causal factors, special emphasis items, and regulatory issues. The

courses li sted below (and many others), as well as seminar and webinar information, can be

accessed from the FAASTeam website at www.faasafety.gov . (Course access requires login

through an existing or creation of a free FAAS Team account .)

 Aircraft Maintenance Documentation for AMTs

 Dirty Dozen: Human Error in Aircraft Maintenance

 Failure to Follow Procedures: Landing Gear Failure

 Human Factors Primer for Aviation Mech anics

 Working Healthy: 8 Steps for Protecting Your Health

 Failure to Follow Procedures: Inspections

 Failure to Follow Procedures: Installation

 Fatigue Countermeasure Training

Other FAA resources:

 “Acceptable Methods, Techniques, and Practices —Aircraft Inspection and Repair ”

(FAA Advisory Circular [AC] 43 .13-1B) contains a Personal Minimums Checklist in

chapter 13 that l ists actions to accomplish before and after maintenance tasks to

reduce maintenance errors.

 Aviation Main tenance Technician Handbook – General (FAA-H-8083 -30) includes an

“Addendum/Human Factors ,” which discusses the human factors -related conditions

behind most maintenance errors . The addendum (which is also called chapter 14)

can be accessed from the FAA’s website at www.faa.gov .

 Aircraft Safety Alerts , including airworthiness directives, maintenance alerts, special

airworthiness information bulletins, and unapproved parts notifications, can be

accessed from www.faa.gov/aircraft/safety/ alerts .

 The Human Factors in Aviation Maintenance Web Portal provides educational

resources, including videos and presentations related to mitigation strategies for

preventing human -performance -related maintenance errors. It can be accessed at

https://www.faa.gov/about/initiatives/maintenance_hf/ .

This NTSB safety alert and others can be accessed from the NTSB’s Safety Alerts web

page at http://www.ntsb.gov/safety/safety -alerts/Pages/default.aspx .