Human Factors in aircraft maintenance

[Corrosion]

Lots of stories, from real life on line maintenance.

#1 fatigue/stress?
Guys towed aircraft from hangar to apron/passenger bridge end of the 12hrs nightshift.If my memory serves right, it wasn´t first night on row. Both guys well experienced and "good" guys overall. Longish, booring towing job during early morning hours end to collision with bridge as guy behind tug steering wheel almost fell to sleep and another guy on brakes was too slow to react due to fatigue. Big damages to a/c engines, and bridge damaged as well. No damages to personnel.

Fatigue is big issue as lots of work is carried out during nights, and long shift patterns. Seems to be quite regular see 7 x 12hrs shifts on row.
I did 12hrs shifts, three on row earlier and later with different company seven on row but they were usually shorter nights. Even i am evening person, can´t say it is easy or light work.

Lots of unnecessary damages or faults due to people are not concentrate on their task. Sometimes it is because distraction, sometimes people are just thinking something else than actual task.
Saw too many times "council work", one individual doing relatively simple task but his/her colleagues buzzing around and creates distraction etc etc...

#2 Maybe lack of knowledge?
Aircraft was flying very first legs after C-check. Aircraft grounded away from home base due to heavy fuel leak from wing, during refuelling.
Found out slat track punctured its "canister" on wing leading edge, causing fuel to leak out.
Cause was wrongly installed/missing bushing/roller which supports slat track.

Same kind of problem found on weekly check, by non type rated mechanic. Part of landing gear retraction mechanism linkages were installed wrong way, actually only one bolt was wrong way. Bolt head chafed nearby linkage badly, fortunately linkage material was softer and bolt head eats its way thru material. Not creating any actual jamming etc etc.

#3 Complacency?
Flap interconnect cables extremely badly damaged, almost broken. Area easily visible on weekly/daily check. Damage noted when cable almost cut, and according to broken strands condition not happened just on last landing. These cables are 3/16 size on that particular a/c.
Reason for cable damage was loose up stop block on flap, this creates big stress for cables as one side flap moves few cm more in than other. This was found after someone thinks "why relatively thick cable almost snapped w/o obvious reason.

#4 Lack of team work, pressure...?
During night shift, fuel control unit was replaced and work was ready for final check and eng run. By oncoming day shift.
Quick double checks were performed and wet run was performed before actual eng start, which ended heavy fuel leak. Fuel inlet fitting was only hand tight and when engine motored, mechanical fuel pump pumps enough pressure to cause big spraying fuel leak.
Nightshift missed loose fitting, as did next shift as well even shift hand over was done. + visual check for installation.
Aircraft needed to service, so pressure to get eng run done was great. Installation was corrected, eng run performed w/o problems and a/c released to service. This was good sign for importance of checks and tests, if a/c released for service w/o leak run... fuel leak all over cowling and engine... real risk for eng fire.

These may be classified differently, think there is not only one answer.

Saw lots of different damages, incidents, problems during my +30 years with general aviation and airline life. Done mistakes by myself as well, but tried to learn from every lessons. Fortunately, never had any serious mistakes, yet, and hopefully i can retire some day without any. Can´t relay self-satisfaction too much, always check, and check again. Ask someone else to check. Ask if you don´t know.