An inspector and mechanic report about miscalculating and subtracting; instead of adding; the rudder...

Attributes
ACN	808775
Time
Date	200810
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	agl single value : 0
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B757-200
Flight Phase	ground : maintenance ground : taxi
Person 1
Affiliation	company : air carrier
Qualification	technician : powerplant technician : airframe technician : inspection authority
Experience	maintenance technician : 9
ASRS Report	808775
Person 2
Affiliation	company : air carrier
Function	maintenance : technician
Qualification	technician : powerplant technician : airframe
Experience	maintenance technician : 21
ASRS Report	808903
Events
Anomaly	aircraft equipment problem : critical maintenance problem : improper maintenance non adherence : published procedure non adherence : far
Independent Detector	other other : 1
Resolutory Action	none taken : detected after the fact
Consequence	other
Factors
Maintenance	contributing factor : schedule pressure contributing factor : briefing performance deficiency : inspection performance deficiency : scheduled maintenance performance deficiency : testing performance deficiency : non compliance with legal requirements
Supplementary
Problem Areas	Maintenance Human Performance Environmental Factor
Primary Problem	Maintenance Human Performance

Narrative:

Performed engineering document. Steps 29 and 30 require you to add the rudder travel distance in the right and left position to get a total free play measurement. In each instance; the mechanic and I subtracted instead of adding. Notified company and the mechanic. Will ensure that the paperwork is read properly and that enough time is taken during the shift to perform the work properly. Supplemental information from acn 808903: while performing engineering document revision J for rudder lower PCU free play check; I miscalculated the free play measurement due to rushing at the end of a double shift. The free play measurement was subtracted instead of added. Re-measured rudder lower PCU free play and found measured free play is within limits per engineering document revision J. I felt fatigue because I had worked a double shift. Time was running out. I had 30 mins to sign off the completed paperwork steps that I had accomplished before I went home for the wkend and my days off. Prior to that; during the shift; there were some distrs around my workplace. There were people who were asked to stay off the airplane several times to ensure accurate readings. There were other crews who kept rushing me to hurry up so they could jack the airplane for a gear swing along with the same people who were asked to stay off the airplane wanting to know every few mins how soon can they get back on the airplane.

Original NASA ASRS Text

Title: AN INSPECTOR AND MECHANIC REPORT ABOUT MISCALCULATING AND SUBTRACTING; INSTEAD OF ADDING; THE RUDDER LOWER PCU TRAVEL DISTANCE IN THE RIGHT AND LEFT POSITION; TO GET A TOTAL FREEPLAY MEASUREMENT; PER THEIR B757-200 ENGINEERING DOCUMENT.

Narrative: PERFORMED ENGINEERING DOCUMENT. STEPS 29 AND 30 REQUIRE YOU TO ADD THE RUDDER TRAVEL DISTANCE IN THE R AND L POS TO GET A TOTAL FREE PLAY MEASUREMENT. IN EACH INSTANCE; THE MECH AND I SUBTRACTED INSTEAD OF ADDING. NOTIFIED COMPANY AND THE MECH. WILL ENSURE THAT THE PAPERWORK IS READ PROPERLY AND THAT ENOUGH TIME IS TAKEN DURING THE SHIFT TO PERFORM THE WORK PROPERLY. SUPPLEMENTAL INFO FROM ACN 808903: WHILE PERFORMING ENGINEERING DOCUMENT REVISION J FOR RUDDER LOWER PCU FREE PLAY CHK; I MISCALCULATED THE FREE PLAY MEASUREMENT DUE TO RUSHING AT THE END OF A DOUBLE SHIFT. THE FREE PLAY MEASUREMENT WAS SUBTRACTED INSTEAD OF ADDED. RE-MEASURED RUDDER LOWER PCU FREE PLAY AND FOUND MEASURED FREE PLAY IS WITHIN LIMITS PER ENGINEERING DOCUMENT REVISION J. I FELT FATIGUE BECAUSE I HAD WORKED A DOUBLE SHIFT. TIME WAS RUNNING OUT. I HAD 30 MINS TO SIGN OFF THE COMPLETED PAPERWORK STEPS THAT I HAD ACCOMPLISHED BEFORE I WENT HOME FOR THE WKEND AND MY DAYS OFF. PRIOR TO THAT; DURING THE SHIFT; THERE WERE SOME DISTRS AROUND MY WORKPLACE. THERE WERE PEOPLE WHO WERE ASKED TO STAY OFF THE AIRPLANE SEVERAL TIMES TO ENSURE ACCURATE READINGS. THERE WERE OTHER CREWS WHO KEPT RUSHING ME TO HURRY UP SO THEY COULD JACK THE AIRPLANE FOR A GEAR SWING ALONG WITH THE SAME PEOPLE WHO WERE ASKED TO STAY OFF THE AIRPLANE WANTING TO KNOW EVERY FEW MINS HOW SOON CAN THEY GET BACK ON THE AIRPLANE.

Data retrieved from NASA's ASRS site as of May 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

An inspector and mechanic report about miscalculating and subtracting; instead of adding; the rudder lower PCU travel distance in the right and left position; to get a total freeplay measurement; per their B757-200 engineering document.