Cruise Altitude Flexibility

One of the key aspects of contrail avoidance is the cruise altitude flexibility, assuming that the aircraft has enough on-board information to determine whether contrail formation can be minimised.

The FLIGHT software has a module that determines the contrail factor, depending on the atmospheric conditions. An option exists to command a climb or descent to a more suitable altitude, although this operation would be subject to air traffic control regulations.

With the FLIGHT software, we can offer detailed environmental and operational performance of any modern commercial aircraft. In this context, we discuss only the benefits of altitude flexibility.


Cruise Altitude Analysis of the Boeing B777-300

Let us analyse the results shown in the graph below, which refers to the Boeing B777-300. The optimal cruise altitude at long-range Mach number (MLM) is the point B; the optimal cruise altitude at the maximum-range Mach number is the point A. In practice, both cases correspond to a flight level FL-350. If the operational point is A, the aircraft can move down to A1 or up to C with a penalty in specific range of about 1%. This is in fact a 4,000 feet flexibility at the same cost that would arise from operating at MLR instead of MMR. Now, if the aircraft reduces its speed to MMR = 0.805 it will gain about 1% in SAR, and can use this gain to pay for its altitude flexibility, which in turn can be used to reduce the contrail factor.

Boeing B777-300 cruise altitude flexibility graph

Cruise altitude analysis of the Boeing B777-300