Narrative:

This is yet another in a series of overweight events. The use of the allowable yet fictitious passenger and baggage weights that the FAA allows the air carrier to use are only half the weight that the FAA's own empirical data has shown to be true. This outbound flight was overweight by approximately 6000 pounds. This was derived from the 'speed low' at V2 +20 indication. Then at initial leveloff 'alpha speed' at the clean 'min-man' bug as determined from the tps. To extinguish the alpha warning the speed bug had to be moved to 255 KTS. Thus by interpolation, using the speed cards gave a weight of 154000 pounds instead of 147800 pounds at that point in the flight. On landing, alpha was shown to be 233 KTS giving a weight of 128000 pounds versus our 'paper weight, of 120000 pounds.' on our return flight the next day, different aircraft, we had similar takeoff indications. But for landing, our alpha speed showed that we actually weighed and landed overweight at approximately 136000 pounds when our paper weight had us at 128000 pounds, an error of nearly 8000 pounds. Observed landing distance put us at M6 on runway 9R instead of the more typical M5 turnoff. I wrote up in the logbook a request for an overweight inspection. I respectfully request that the flight department put out a formal request of all pilots of our air carrier that all 'speed low' and 'alpha speed' indications be documented and that an approved use of the speed bug to determine actual aircraft weight, based on the observation of these 2 real time empirical numbers, be created. If the use of the FAA's N8300.112 report are valid, then there should be no cases of overweight aircraft. My own random sampling has shown that the opposite will be true. Disorganized accounting methods and the denial that the flying public is larger and carries more on to our planes puts all of us and our air carrier at risk. Do we need an engine failure on one of these flts to do a 'cost benefit analysis' or can we, as proactive pilots and safety mgrs, do something in advance? Callback conversation with reporter revealed the following information: reporter clarified that the means by which he determined the actual weight of the aircraft -- as compared to the weights provided by the company in compliance with FAA approved procedures -- was the aircraft flight data computer system which advises when selected airspds do not comply with angle of attack requirements for the current flap setting. By determining the speed at which the angle of attack requirements were satisfied, the actual weight of the aircraft could be determined and compared to the same computation based on the final load planning weights issued by the company. Reporter stressed strongly that he felt the company is using FAA approved methods of determining aircraft weight through canned assumptions regarding the weight of passenger and baggage, while fully aware the actual weights are significantly higher. The reporter alleges, when multiplied by a couple of hundred passenger, the results can be a significant discrepancy between planned and actual weight, enough to alter the required airspeed to meet performance specifications for all phases of flight.

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Original NASA ASRS Text

Title: CAPT OF MD83 DISCOVERS CALCULATED WT OF ACFT IS LESS THAN ACTUAL AS A RESULT OF UNDERSPD WARNINGS GENERATED BY THE ACFT'S FMS PERFORMANCE COMPUTER.

Narrative: THIS IS YET ANOTHER IN A SERIES OF OVERWT EVENTS. THE USE OF THE ALLOWABLE YET FICTITIOUS PAX AND BAGGAGE WTS THAT THE FAA ALLOWS THE ACR TO USE ARE ONLY HALF THE WT THAT THE FAA'S OWN EMPIRICAL DATA HAS SHOWN TO BE TRUE. THIS OUTBOUND FLT WAS OVERWT BY APPROX 6000 LBS. THIS WAS DERIVED FROM THE 'SPD LOW' AT V2 +20 INDICATION. THEN AT INITIAL LEVELOFF 'ALPHA SPD' AT THE CLEAN 'MIN-MAN' BUG AS DETERMINED FROM THE TPS. TO EXTINGUISH THE ALPHA WARNING THE SPD BUG HAD TO BE MOVED TO 255 KTS. THUS BY INTERPOLATION, USING THE SPD CARDS GAVE A WT OF 154000 LBS INSTEAD OF 147800 LBS AT THAT POINT IN THE FLT. ON LNDG, ALPHA WAS SHOWN TO BE 233 KTS GIVING A WT OF 128000 LBS VERSUS OUR 'PAPER WT, OF 120000 LBS.' ON OUR RETURN FLT THE NEXT DAY, DIFFERENT ACFT, WE HAD SIMILAR TKOF INDICATIONS. BUT FOR LNDG, OUR ALPHA SPD SHOWED THAT WE ACTUALLY WEIGHED AND LANDED OVERWT AT APPROX 136000 LBS WHEN OUR PAPER WT HAD US AT 128000 LBS, AN ERROR OF NEARLY 8000 LBS. OBSERVED LNDG DISTANCE PUT US AT M6 ON RWY 9R INSTEAD OF THE MORE TYPICAL M5 TURNOFF. I WROTE UP IN THE LOGBOOK A REQUEST FOR AN OVERWT INSPECTION. I RESPECTFULLY REQUEST THAT THE FLT DEPT PUT OUT A FORMAL REQUEST OF ALL PLTS OF OUR ACR THAT ALL 'SPD LOW' AND 'ALPHA SPD' INDICATIONS BE DOCUMENTED AND THAT AN APPROVED USE OF THE SPD BUG TO DETERMINE ACTUAL ACFT WT, BASED ON THE OBSERVATION OF THESE 2 REAL TIME EMPIRICAL NUMBERS, BE CREATED. IF THE USE OF THE FAA'S N8300.112 RPT ARE VALID, THEN THERE SHOULD BE NO CASES OF OVERWT ACFT. MY OWN RANDOM SAMPLING HAS SHOWN THAT THE OPPOSITE WILL BE TRUE. DISORGANIZED ACCOUNTING METHODS AND THE DENIAL THAT THE FLYING PUBLIC IS LARGER AND CARRIES MORE ON TO OUR PLANES PUTS ALL OF US AND OUR ACR AT RISK. DO WE NEED AN ENG FAILURE ON ONE OF THESE FLTS TO DO A 'COST BENEFIT ANALYSIS' OR CAN WE, AS PROACTIVE PLTS AND SAFETY MGRS, DO SOMETHING IN ADVANCE? CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR CLARIFIED THAT THE MEANS BY WHICH HE DETERMINED THE ACTUAL WT OF THE ACFT -- AS COMPARED TO THE WTS PROVIDED BY THE COMPANY IN COMPLIANCE WITH FAA APPROVED PROCS -- WAS THE ACFT FLT DATA COMPUTER SYS WHICH ADVISES WHEN SELECTED AIRSPDS DO NOT COMPLY WITH ANGLE OF ATTACK REQUIREMENTS FOR THE CURRENT FLAP SETTING. BY DETERMINING THE SPD AT WHICH THE ANGLE OF ATTACK REQUIREMENTS WERE SATISFIED, THE ACTUAL WT OF THE ACFT COULD BE DETERMINED AND COMPARED TO THE SAME COMPUTATION BASED ON THE FINAL LOAD PLANNING WTS ISSUED BY THE COMPANY. RPTR STRESSED STRONGLY THAT HE FELT THE COMPANY IS USING FAA APPROVED METHODS OF DETERMINING ACFT WT THROUGH CANNED ASSUMPTIONS REGARDING THE WT OF PAX AND BAGGAGE, WHILE FULLY AWARE THE ACTUAL WTS ARE SIGNIFICANTLY HIGHER. THE RPTR ALLEGES, WHEN MULTIPLIED BY A COUPLE OF HUNDRED PAX, THE RESULTS CAN BE A SIGNIFICANT DISCREPANCY BTWN PLANNED AND ACTUAL WT, ENOUGH TO ALTER THE REQUIRED AIRSPD TO MEET PERFORMANCE SPECS FOR ALL PHASES OF FLT.

Data retrieved from NASA's ASRS site as of July 2007 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.