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1       Introduction 

Modified Reserves 

This simulation will focus on the specific functionality of modified reserves, and how that fuel saving measure can be employed during practical flight planning. 

We estimate that this will take 2 minutes to complete.

2       Detailed Explanation 

Modified Reserve Functionality

This module will demonstrate the function and benefits of Modified Reserves.  To highlight the fuel savings we will begin with an already computed flight, note the fuel requirement for that flight, and then show the difference with Modified Reserves.


Modified Reserves allow for reduction in required fuel for international flights, in accordance with fuel saving authorizations similar to FAA Operations Specification B043.

Note that the original flight plan requires 5,834lbs / 30min of Holding Fuel, and 5,999lbs / 31min of Reserve Fuel

Interaction 1

Interaction 1 Click the Reserve green arrow button.

Interaction 1

Interaction 1 Click the Policy dropdown button.

Interaction 1

Interaction 1 Click the Policy (Modified Reserves) list item.

Interaction 1

Interaction 1 Click the Compute button.

With Modified Reserves, the fuel requirements are 0lbs / 0min Holding Fuel, and 8,655 / 45min Reserve Fuel.

This is a savings of 3,178lbs / 16min of fuel.

Interaction 1

Interaction 1 Click the Fuel >> expansion button.

The original intent of the Modified Reserves, was to meet the requirements of fuel saving authorization, similar to FAA Operations Specification B043.  As such, when Modified Reserves are used, the system eliminates Holding Fuel, and changes the Reserve to a static 45min of fuel.


Another aspect of this function is the ability to specify sections of the route which transit Class II Airspace.  The FAA OpSpec B043 requires fuel for "10 percent of that portion of the enroute time (between the departure airport and the airport to which it was released) where the aircraft's position cannot be "reliably fixed" at least once each hour."


To achieve this, the system allows you to enter waypoint pairs for the Class II segments.

Interaction 1 Click the Mod Resv dropdown button.

Interaction 1

Interaction 1 Click the PPT list item.

Note the description below, indicating the first modified reserve waypoint. 

Interaction 1

Interaction 1 Click the Second Mod Resv dropdown button.

Interaction 1

Interaction 1 Click the RAJ list item.

Interaction 1

Interaction 1 Click the Compute button.

With the addition of the Modified Reserve Waypoints, simulating Class II Airspace, the fuel requirement is now 9,227lbs / 48min of Reserve Fuel.


Additional information:

Policy 26 (MOD RES) is 45 min * TOD fuel flow + the mod res fuel calculation if waypoints are selected.  This comes from:

2)    When the same flight is conducted under OpSpec B043, a somewhat smaller fuel load is required. Even though the time en route is equal for both flights, the lower takeoff weight of the OpSpec B043 flight results in a lower en route fuel burn. The en route reserve fuel is 18 minutes ([3 hours x 60 minutes = 180 minutes] x 10 percent = 18 minutes). At 16,000 pounds per hour, 18 minutes is 4,800 pounds [18/60 x 16,000]. The international reserve fuel for the OpSpec B043 flight is 45 minutes at normal cruising fuel consumption (for the weight and altitude at which the flight reaches the alternate); therefore, 45 minutes at 16,000 pounds per hour is 12,000 pounds.