Inside the FMS

Benefits of NGFMS Gold Package - Cost Index and ECON Speeds

The NGFMS Gold package for the Embraer E-Jets (E170/175/190 and 195) adds several airline-specific capabilities to the Basic NGFMS that deliver quantifiable and measurable value to airlines operating these aircraft. NGFMS Gold offers three main benefits to airline operators:

      1. Cost Index (CI) and ECON Speeds
      2. Wind Trade Steps evaluation
      3. Optimum (Off-Idle) descent path creation and management capability

This article will focus on Cost Index and ECON Speeds and what crews need to know to take advantage of this feature.

Cost Index (and corresponding FMS calculated ECON speeds) is designed to minimize the total operating cost for a flight. CI is defined as the ratio of time-related cost of the flight to the cost of fuel.

ci

Simply put, crews will use a low CI value when fuel costs are relatively high compared to time-related costs. On the flip side, when fuel costs are low relative to time-related costs, crews will see a higher CI value. The FMS accepts CI values ranging from 0 to 999. A value of “0” will result in an ECON speed calculation that achieves maximum range and minimum fuel burn. Conversely, a CI of “999” will result in the FMS commanding maximum flight envelope speeds. In practice, the CI value most likely used will be somewhere in between these extremes.

Through the calculation of this single parameter, the Cost Index, the dispatcher can provide a crew with an input to the FMS that enables it to calculate and control the climb, cruise, and descent speed schedule to match the operation of each flight to the desired cost optimization strategy. Moreover, if conditions change during flight, a different cost index can be sent by the dispatcher to the crew and entered in the FMS to realign the trip cost to constantly changing conditions such as known delays in the terminal area or the need to fly faster due to a departure delay.

ECON Speeds

ECON speeds are different than Long Range Cruise (LRC) speeds in that ECON speeds take advantage of the atmospheric model included in NGFMS and accounts for winds. A tailwind will result in reduced ECON speeds and a headwind will result in increased ECON speeds. ATC has no visibility to ECON speeds and, as always, ATC speed assignments take precedent over FMS calculated speeds.

The CI value is entered on the PERFORMANCE INIT 3/3 page on LSK 4L. Ensure “ECON” is selected on 1L, 2L, 3L for the respective climb, cruise, and descent speeds as shown in Figure 1. Note that the default COST INDEX value is 10.

econ

Through the use of Cost Index and ECON speeds, operators can now sit back, relax, and enjoy the cost savings.

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