When the cockpit performance computer fails to provide takeoff data; flight crew of B737-500 uses da...

Attributes
ACN	736751
Time
Date	200704
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	agl single value : 0
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B737-500
Operating Under FAR Part	Part 121
Flight Phase	ground : preflight
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 70
ASRS Report	736751
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : critical non adherence : far non adherence : published procedure
Independent Detector	other flight crewa
Resolutory Action	none taken : detected after the fact none taken : anomaly accepted
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft Company
Primary Problem	Company

Narrative:

At pushback; first officer was unable to get performance computer to compute takeoff data. He passed it to our jumpseater. He was also unable to get to the takeoff page. I called dispatch after a quick glance at the performance computer. Dispatch gave us the numbers for runway 25R. Data was bleeds off. We made more unsuccessful attempts to get the performance computer to calculate the numbers on the taxi out. We made a normal takeoff. After leveloff; I tried again to get the data and noticed the aircraft was overweight for the runway (even bleeds off). We had failed to notice that our weight was bracketed. Our actual weight was 119.2 and the runway limit was 111.8! I am unsure how dispatch was able to calculate speeds V1 152; vr 155; V2 159 and 3030 ft stopping margin. Modify the performance computer to give an error message when trying to get takeoff data when overweight for the runway selected. Currently; the performance computer just sits quietly and will not advance. Callback conversation with reporter revealed the following information: the reporter advised that the cockpit computer was actually working; but that when the data input exceeded legal values; the program simply refused to continue the computation process. Because it displayed no error code; the flight crew assumed it was a hardware malfunction. This led them to employ the erroneous data provided by their dispatcher.

Original NASA ASRS Text

Title: WHEN THE COCKPIT PERFORMANCE COMPUTER FAILS TO PROVIDE TKOF DATA; FLT CREW OF B737-500 USES DATA SUPPLIED BY DISPATCHER. LATER DISCOVER THAT DATA WAS INCORRECT AND THAT TKOF WAS MADE APPROX 8000 LBS OVER ALLOWABLE RWY LIMIT.

Narrative: AT PUSHBACK; FO WAS UNABLE TO GET PERFORMANCE COMPUTER TO COMPUTE TKOF DATA. HE PASSED IT TO OUR JUMPSEATER. HE WAS ALSO UNABLE TO GET TO THE TKOF PAGE. I CALLED DISPATCH AFTER A QUICK GLANCE AT THE PERFORMANCE COMPUTER. DISPATCH GAVE US THE NUMBERS FOR RWY 25R. DATA WAS BLEEDS OFF. WE MADE MORE UNSUCCESSFUL ATTEMPTS TO GET THE PERFORMANCE COMPUTER TO CALCULATE THE NUMBERS ON THE TAXI OUT. WE MADE A NORMAL TKOF. AFTER LEVELOFF; I TRIED AGAIN TO GET THE DATA AND NOTICED THE ACFT WAS OVERWT FOR THE RWY (EVEN BLEEDS OFF). WE HAD FAILED TO NOTICE THAT OUR WT WAS BRACKETED. OUR ACTUAL WT WAS 119.2 AND THE RWY LIMIT WAS 111.8! I AM UNSURE HOW DISPATCH WAS ABLE TO CALCULATE SPDS V1 152; VR 155; V2 159 AND 3030 FT STOPPING MARGIN. MODIFY THE PERFORMANCE COMPUTER TO GIVE AN ERROR MESSAGE WHEN TRYING TO GET TKOF DATA WHEN OVERWT FOR THE RWY SELECTED. CURRENTLY; THE PERFORMANCE COMPUTER JUST SITS QUIETLY AND WILL NOT ADVANCE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE REPORTER ADVISED THAT THE COCKPIT COMPUTER WAS ACTUALLY WORKING; BUT THAT WHEN THE DATA INPUT EXCEEDED LEGAL VALUES; THE PROGRAM SIMPLY REFUSED TO CONTINUE THE COMPUTATION PROCESS. BECAUSE IT DISPLAYED NO ERROR CODE; THE FLT CREW ASSUMED IT WAS A HARDWARE MALFUNCTION. THIS LED THEM TO EMPLOY THE ERRONEOUS DATA PROVIDED BY THEIR DISPATCHER.

Data retrieved from NASA's ASRS site as of January 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.

When the cockpit performance computer fails to provide takeoff data; flight crew of B737-500 uses data supplied by dispatcher. Later discover that data was incorrect and that takeoff was made approximately 8000 pounds over allowable runway limit.