Narrative:

'B' flight attendant (flight attendant) reported fumes of burning plastic in aft galley; likely source gasper vents. I directed the first officer (first officer) to open the smoke/fire/fumes on the aircraft checklist in case we chose to go that path. The first officer checked in again with the 'B' flight attendant to gain more information if the fumes persisted. Once we were confident the smell was not the result of deicing; we donned oxygen masks in accordance with the immediate actions; and initiated the smoke/fire/fumes on the aircraft checklist. To shorten up the story; we created a plan to recover the aircraft at the nearest suitable field. I continued to fly and talk with ATC and he continued to manage the checklists and communication with all parties except ATC. As the first officer calculated landing data; I provided him with a landing weight of 122;000 pounds. He seemed confused by this number but had little time to process why as we were very busy running the smoke/fire/fumes on the aircraft checklist (latter portion of trying to identification the source of smoke); descent checklist; and communicating with the cabin; ATC; and flight ops. Only after landing did I realize the error calculating landing weight and approach speeds. Since neither one of us cleared out the FMC routing; the enroute fuel burn calculation contributed to an unrealistic landing weight (122;000 vice 142;000). Had either one of us been in the green we would have simply used the gross weight as landing was imminent. Post-flight; we calculated that we introduced a 10-knot error into the approach calculations. I do not believe we approached the planned (erroneous) speed until over the threshold. This was the first officer's first leg after an extended time off and only my second trip after a six-week absence. Crew coordination could have been better. Upon receiving a clearance direct to the airport; I programmed and executed the clearance while the first officer was otherwise occupied. He was notified of our routing and altitudes whenever he returned to the ATC frequency. However; I/we could have also changed the fmcs destination to the new airport. Assertiveness and backing each other up: I feel that our expedited recovery reduced/prevented the time to think of what we had already accomplished and if anything was left out. As a result; our ability to trap the weight calculation error was nullified. The first officer may have dismissed the weight calculation inconsistency because a) of my perceived experience and b) task loading. The ongoing communication demands with flight ops; cabin crew; and in his spare time; ATC. We should have managed the FMC programmed routing in a manner to avoid any confusion on fuel burn or landing weights. Enter the revised destination on route page 1. Continue to talk with the other flight crew member to flesh out concerns or misunderstandings.

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Original NASA ASRS Text

Title: B737-700 flight crew reported making an error when figuring landing gross weight during their return to departure airport because of fumes in the aircraft.

Narrative: 'B' Flight Attendant (FA) reported fumes of burning plastic in aft galley; likely source gasper vents. I directed the First Officer (FO) to open the Smoke/Fire/Fumes on the Aircraft Checklist in case we chose to go that path. The FO checked in again with the 'B' FA to gain more information if the fumes persisted. Once we were confident the smell was not the result of deicing; we donned oxygen masks in accordance with the immediate actions; and initiated the Smoke/Fire/Fumes on the Aircraft Checklist. To shorten up the story; we created a plan to recover the aircraft at the nearest suitable field. I continued to fly and talk with ATC and he continued to manage the checklists and communication with all parties except ATC. As the FO calculated landing data; I provided him with a landing weight of 122;000 pounds. He seemed confused by this number but had little time to process why as we were very busy running the Smoke/Fire/Fumes on the Aircraft Checklist (latter portion of trying to ID the source of smoke); Descent Checklist; and communicating with the cabin; ATC; and Flight Ops. Only after landing did I realize the error calculating landing weight and approach speeds. Since neither one of us cleared out the FMC routing; the enroute fuel burn calculation contributed to an unrealistic landing weight (122;000 vice 142;000). Had either one of us been in the Green we would have simply used the gross weight as landing was imminent. Post-flight; we calculated that we introduced a 10-knot error into the approach calculations. I do not believe we approached the planned (erroneous) speed until over the threshold. This was the FO's first leg after an extended time off and only my second trip after a six-week absence. Crew Coordination could have been better. Upon receiving a clearance direct to the airport; I programmed and executed the clearance while the FO was otherwise occupied. He was notified of our routing and altitudes whenever he returned to the ATC frequency. However; I/we could have also changed the FMCs destination to the new airport. Assertiveness and backing each other up: I feel that our expedited recovery reduced/prevented the time to think of what we had already accomplished and if anything was left out. As a result; our ability to trap the weight calculation error was nullified. The FO may have dismissed the weight calculation inconsistency because a) of my perceived experience and b) task loading. The ongoing communication demands with Flight Ops; Cabin crew; and in his spare time; ATC. We should have managed the FMC programmed routing in a manner to avoid any confusion on fuel burn or landing weights. Enter the revised destination on Route page 1. Continue to talk with the other Flight Crew Member to flesh out concerns or misunderstandings.

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.