Narrative:

I had to dispatch a ferry flight to mke with flaps down at 20 degrees; at or below 15000 feet and 200 knots with no prolonged flight in icing conditions. There was an icing airmet over roc from the freezing level to FL240. Freezing level was 9000 feet over roc and they had a broken later at 11000. Mke had a few at 5000 with broken 25000. Over michigan; lan and mkg were clear; and looking at a satellite view I could see clear sky from abeam eri all the way to the wi shoreline of lake michigan; and I knew they should be able to descend to get below the clouds and avoid the few low clouds near milwaukee. So; I built a route to take them across michigan at 6000 feet and the captain agreed we would stay out of icing conditions enroute to mke. At first I ran the flight plan using the standard performance data; to be sure my flight plan was viable. I also wrote down the speed and the burn for that performance data. I then re-ran the calculator using flaps 20 data; but received a 'descent performance not available' error. I then re-ran the calculator using hold; gear down; 250; lrc and medium large transport bay performance data; and recorded the speeds and burns for each of the results. Since 200 knots was my restriction; I chose to use hold performance data; and to 'pad' the hold fuel to be sure the flight could be completed. I also listed an alternate in case the mke cloud forecast was not accurate; they would have a place to go with no icing conditions. All this took time from doing other revenue releases; and put me behind in my regular work. I had to work quickly to get caught up; and I didn't realize that I had forgotten to calculate the flaps 20 landing distance. I did calculated it when the flight was on the arrival at mke; and came up with a calculated required distance of 3920 with 8012 feet available for landing runway 07R; which is what mke was using at the time. The captain did not query about this; but it is something that I usually put in the remarks section of a release with flaps that are limited to 20 degrees. I did ask the crew how the cloud layer looked; as well as how they were doing on fuel burn; about 1/3 of the way through the flight. At that time they were just coming out from under the clouds; and the fob was 500 hundred pounds above what the flight plan showed they should have. So I was feeling confident the flight would be successful; and that they had sufficient fuel on board. It was not until they finally landed; and I saw that the actual burn was about 1300 pounds higher than I had planned them for that I became concerned. At this point I was reminded by one of my fellow dispatchers about a training bulletin that had been issued last summer which addressed the use of non-standard cruise performance. I then realized that I should have also changed the fuel policy; in order to adjust the reserve fuel for the non-standard performance. I am not sure why I had the calculation error when using flaps 20 performance data; but in retrospect; I probably should have used gear down performance data; as that would have been closer to the actual burn. So; by using a performance data based on speed; I ended up planning a fuel burn which was less than actual; and a reserve fuel that was about half of what it should have been. When I later ran a 'what if' scenario; with flaps 20 in the fob [fuel on board] window; it calculated a reserve of 3017 pounds compared to my standard 1700. I ran a 'what if' scenario with gear down performance data and flaps 20 fuel over destination; and that came up with a burn of 5930 (5700 actual); a reserve of 3060; and an alternate burn of 1430 for a ramp fuel of 12170. My release called for a ramp fuel of 8650 about 3500 pounds short of what it should have been. The alternate plus reserve came out to 4490 and actual landing fuel was 3400; 1090 short. I suppose if you take the alternate off (since it was technically not required); the flight did land with reserve on board; but since I did not remove the alternate; the flight did land with below legal fuel requirements.I need to periodically review the training bulletins that have been issued. By default; I have not had to do any ferry flights; or flights that required use of the non-standard cruise performance; so I forgot that this change had taken place. I should also have used the more conservative gear down performance when the calculation error came up for the flaps 20 data.

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Original NASA ASRS Text

Title: Dispatcher reported using alternative means to calculate the fuel required for a flaps down ferry flight. He discovered after the flight that the fuel burn and reserve calculations were not correct.

Narrative: I had to dispatch a ferry flight to MKE with flaps down at 20 degrees; at or below 15000 feet and 200 knots with no prolonged flight in icing conditions. There was an icing AIRMET over ROC from the freezing level to FL240. Freezing level was 9000 feet over ROC and they had a broken later at 11000. MKE had a few at 5000 with broken 25000. Over Michigan; LAN and MKG were clear; and looking at a satellite view I could see clear sky from abeam ERI all the way to the WI shoreline of Lake Michigan; and I knew they should be able to descend to get below the clouds and avoid the few low clouds near Milwaukee. So; I built a route to take them across Michigan at 6000 feet and the Captain agreed we would stay out of icing conditions enroute to MKE. At first I ran the flight plan using the standard performance data; to be sure my flight plan was viable. I also wrote down the speed and the burn for that performance data. I then re-ran the calculator using flaps 20 data; but received a 'Descent Performance Not Available' error. I then re-ran the calculator using HOLD; GEAR DOWN; 250; LRC AND MLG BAY performance data; and recorded the speeds and burns for each of the results. Since 200 knots was my restriction; I chose to use HOLD performance data; and to 'pad' the hold fuel to be sure the flight could be completed. I also listed an alternate in case the MKE cloud forecast was not accurate; they would have a place to go with no icing conditions. All this took time from doing other revenue releases; and put me behind in my regular work. I had to work quickly to get caught up; and I didn't realize that I had forgotten to calculate the flaps 20 landing distance. I did calculated it when the flight was on the arrival at MKE; and came up with a calculated required distance of 3920 with 8012 feet available for landing runway 07R; which is what MKE was using at the time. The Captain did not query about this; but it is something that I usually put in the remarks section of a release with flaps that are limited to 20 degrees. I did ask the crew how the cloud layer looked; as well as how they were doing on fuel burn; about 1/3 of the way through the flight. At that time they were just coming out from under the clouds; and the FOB was 500 hundred pounds above what the Flight plan showed they should have. So I was feeling confident the flight would be successful; and that they had sufficient fuel on board. It was not until they finally landed; and I saw that the actual burn was about 1300 pounds higher than I had planned them for that I became concerned. At this point I was reminded by one of my fellow dispatchers about a training bulletin that had been issued last summer which addressed the use of Non-Standard Cruise Performance. I then realized that I should have also changed the Fuel Policy; in order to adjust the reserve fuel for the non-standard performance. I am not sure why I had the calculation error when using Flaps 20 performance data; but in retrospect; I probably should have used Gear Down performance data; as that would have been closer to the actual burn. So; by using a performance data based on speed; I ended up planning a fuel burn which was less than actual; and a reserve fuel that was about half of what it should have been. When I later ran a 'what if' scenario; with Flaps 20 in the FOB [fuel on board] window; it calculated a reserve of 3017 pounds compared to my standard 1700. I ran a 'what if' scenario with Gear Down Performance data and Flaps 20 Fuel over destination; and that came up with a burn of 5930 (5700 actual); a reserve of 3060; and an alternate burn of 1430 for a ramp fuel of 12170. My release called for a ramp fuel of 8650 about 3500 pounds short of what it should have been. The alternate plus reserve came out to 4490 and actual landing fuel was 3400; 1090 short. I suppose if you take the alternate off (since it was technically not required); the flight did land with reserve on board; but since I did not remove the alternate; the flight did land with below legal fuel requirements.I need to periodically review the training bulletins that have been issued. By default; I have not had to do any ferry flights; or flights that required use of the Non-Standard Cruise Performance; so I forgot that this change had taken place. I should also have used the more conservative Gear Down performance when the calculation error came up for the Flaps 20 data.

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.