Step Climbs?

[captain420 3,099]

I first encountered this message in my FMC while flying the PMDG 777... I was enroute with my flight level set to FL350, then during that time I looked at the PROG page and it says start STEP CLIMB now,  and I look at the LEGS page on my FMC to see that the next few set of waypoints show FL390. Since I never messed with step climbs before or don't understand how it works, I just continued my flight staying at FL350 without any problems. It was a long flight so I didn't want to risk messing it up, but does anyone know what I am suppose to do when I see this message? I am assuming that I dial my altitude to FL390 and hit the button to initiate the step climb and thats all?

[Captain Kevin 586]

Basically. By default, the step altitude is set to 4,000 feet, although I think generally speaking, you'd climb every 2,000 feet. You'd need to set this up in the FMC under step size. By default, it would say ICAO. The idea is that you burn less fuel at higher altitudes, but you're too heavy initially to get to flight level 390 right away, so you'd start at flight level 350, burn some fuel off, and work your way up.

[Sartanius 399]

Hi Aaron,

Between FL290 and FL410 the airspace is divided into alternating westbound (even) and eastbound (odd) flight levels, each separated vertically by 1000 feet.  This arrangement is referred to as Reduced Vertical Separation Minima (RVSM).  I believe either China or Russia was the last country to finally adopt RVSM, so now virtually the entire worldwide airspace is operated in this fashion.  Prior to RVSM, flight levels were separated vertically by 2000 feet, primarily due to barometric altimeters suffering from reduced accuracy at higher altitudes.  Due to improvement in altitude measuring avionics/instruments in modern aircraft today the flight level minima was reduced to 1000 feet (RVSM) to allow for essentially twice as many aircraft traveling east and west in the same airspace.

As Kevin explained above, aircraft can burn fuel more efficiently the higher they go, but the optimal fuel burn altitude is determined mainly by gross weight.  So, early in a flight the optimal altitude might be, say 34000.  After sufficient fuel burns off and the gross weight goes down, the aircraft reaches a position where the optimal fuel burn efficiency would now be achieved at 36,000 ft.  Flight planning schedules these points along a route where it is recommended to climb 2000 ft. (to the next RVSM flight level in the direction of flight) to obtain more optimal fuel burn efficiency, and these are called step climbs.  It is recommended to follow the guidance.

I'm sure I've probably missed something or misstated a fact or two since I'm writing this general description off the top of my head.  Folks are encouraged to step in and enhance as required.