Narrative:

I have seen; on numerous aircraft over the past several trips; a significant error occur in the aircraft's displayed final weight that could easily lead to crews using takeoff data based on a weight that is less than the displayed aircraft's final weight.on many different flights; I have followed the correct procedure - loaded the final weights; confirmed the weight change from the printed manifest matches (roughly) the change in the FMC; and requested takeoff data based on our new; final weight. The takeoff data is received; printed; verified; and then accepted on the takeoff page.here is where the error occurs. For some reason; on several flights (including the one referenced in this report); after accepting the takeoff data; the displayed weight of the aircraft will bump up spontaneously - anywhere from 600lbs to 2700lbs higher. To be clear - this happens without any prompts; without any receipt of new final weights; and without any notification. It just changes to a higher weight on its own. I have only seen it occur after the takeoff data has already been loaded.examples I have documented since first noticing this:- [date and tail number]; ZZZ - ZZZ1. Weight jumped up about 500 pounds after loading takeoff data.- [date and tail number]; ZZZ2 - ZZZ3. Weight jumped up after loading takeoff data (didn't document increase).- [date and tail number]; ZZZ3 - ZZZ. Planned weight was 168;700. Got final weights. Weight dropped to 166;900. Loaded takeoff data based on 166;900. Within a minute after accepting the takeoff data; the displayed aircraft weight jumped up on its own to 169;600.- [date and tail number]; ZZZ - ZZZ1. Loaded the final weights (this brought the weight to 166;900 pounds) and we had the time to wait (for more than 5 minutes) to see if the change would happen. At first; it didn't. I then requested; received; and accepted the takeoff data. Then; about a minute later; the weight jumped from 166;900 to 167;600 on its own. The captain witnessed this change.- [date and tail number]; ZZZ4 - ZZZ. As before; after accepting the takeoff data; the weight jumped on its own by 600 pounds.to be clear; I am seeing spontaneous; un-prompted weight increases after accepting the takeoff data that puts the final; actual aircraft weight higher than the weight being used for the reduced thrust takeoff.other observations I have noticed to date regarding this:- it seems to be occurring most often on the newer aircraft.- it does not happen every time on the same airplane. On [date and tail number]; it did happen. But; when flying [tail number] again on [date]; it did not happen.- it does not happen on every single flight. Some aircraft I flew recently where there was no observed change.to reiterate; there is some anomaly that increases the aircraft weight above the planned takeoff weight without alerting the crew. I am seeing it happen often; but not every time. If crews do not catch the discrepancy when reviewing takeoff data during the before takeoff checklist; we could have many flights departing with inaccurate takeoff data system wide.

Related reports:

Google
 

Original NASA ASRS Text

Title: B737 First Officer reported observing spontaneous errors in FMC weight displays on multiple flights.

Narrative: I have seen; on numerous aircraft over the past several trips; a significant error occur in the aircraft's displayed final weight that could easily lead to crews using takeoff data based on a weight that is less than the displayed aircraft's final weight.On many different flights; I have followed the correct procedure - loaded the final weights; confirmed the weight change from the printed manifest matches (roughly) the change in the FMC; and requested takeoff data based on our new; final weight. The takeoff data is received; printed; verified; and then accepted on the takeoff page.Here is where the error occurs. For some reason; on several flights (including the one referenced in this report); after accepting the takeoff data; the displayed weight of the aircraft will bump up spontaneously - anywhere from 600lbs to 2700lbs higher. To be clear - this happens WITHOUT any prompts; WITHOUT any receipt of new final weights; and WITHOUT any notification. It just changes to a higher weight on its own. I have only seen it occur after the takeoff data has already been loaded.Examples I have documented since first noticing this:- [date and tail number]; ZZZ - ZZZ1. Weight jumped up about 500 pounds after loading takeoff data.- [date and tail number]; ZZZ2 - ZZZ3. Weight jumped up after loading takeoff data (didn't document increase).- [date and tail number]; ZZZ3 - ZZZ. Planned weight was 168;700. Got final weights. Weight dropped to 166;900. Loaded takeoff data based on 166;900. Within a minute after accepting the takeoff data; the displayed aircraft weight jumped up on its own to 169;600.- [date and tail number]; ZZZ - ZZZ1. Loaded the final weights (this brought the weight to 166;900 LBS) and we had the time to wait (for more than 5 minutes) to see if the change would happen. At first; it didn't. I then requested; received; and accepted the takeoff data. Then; about a minute later; the weight jumped from 166;900 to 167;600 on its own. The captain witnessed this change.- [date and tail number]; ZZZ4 - ZZZ. As before; after accepting the takeoff data; the weight jumped on its own by 600 LBS.To be clear; I am seeing SPONTANEOUS; UN-PROMPTED weight increases AFTER accepting the takeoff data that puts the final; actual aircraft weight HIGHER than the weight being used for the reduced thrust takeoff.Other observations I have noticed to date regarding this:- It seems to be occurring most often on the newer aircraft.- It does NOT happen every time on the same airplane. On [date and tail number]; it DID happen. But; when flying [tail number] again on [date]; it did NOT happen.- It does not happen on every single flight. Some aircraft I flew recently where there was no observed change.To reiterate; there is some anomaly that increases the aircraft weight above the planned takeoff weight without alerting the crew. I am seeing it happen often; but not every time. If crews do not catch the discrepancy when reviewing takeoff data during the before takeoff checklist; we could have many flights departing with inaccurate takeoff data system wide.

Data retrieved from NASA's ASRS site 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.