Copyright Avfacts 1998.
Step climb calcs page 1.
Calculating step climb position.
General
There are times when it is a good idea to climb to a higher altitude whilst enroute. This could be to get an
increased tail wind/decreased head wind, to reduce the fuel flow, or to escape from turbulence. Either way, the
new flight level you wish to cruise at may not be available immediately, and you may have to delay the step
climb until the aircraft GW is reduced to a suitable level.
We will be referencing page 2-14 of the B727 manual when undertaking step climb calculations.
Points to remember:
•
•
•
Manual page 2-2a, para 2 states that an abbreviated method to be used in step climb calculations is to
allow 50 kg/1, 000 ft of step climb to account for the extra fuel burnt in the climb. No distance need be
calculated for the step climb zone. (ie: the aircraft is suddenly at the new level having burnt 50 kg of fuel
per thousand feet. No climb time need be allowed for either.
A step climb is different from a “drift climb” technique in that the step climb is deliberately delayed until
the point when a climb can be made directly to the new level at climb speed (Mach 0.78) at climb thrust.
A drift climb occurs at cruise power, and cruise speed.
These are usually stand alone questions in ATPL exams, though you may incorporate them in a large
normal operations flight plan if you feel it would reduce the total flight fuel.
Example 1.
A B727 is tracking from Auckland (New Zealand) to Hobart on ERC H5 route L513. At TopC (150 DME
Auckland) FL310 the aircraft begins to cruise at Mach 0.80 at a gross weight of 75, 000 kg, in ISA +10
conditions. The wind is 115 kt HEAD.
Turbulence begins to increase as a result of a forecast upper level jetstream with a core centred at FL330.
The Captain wishes to climb into the smooth air reported at FL350 as soon as possible.
Assuming the aircraft continues at Mach 0.80/FL310 until a climb to FL350 can be commenced, and that
Mach 0.80 schedule will be used on reaching FL350 where the temperature is ISA +10, at what minimum
distance past TopC can the climb to FL350 be commenced ?
ISA +10
72, 900 kg
FL350
EMZW
74
M 0.80
Step climb
fuel 200 kg
Start climb GW
73, 100 kg
TopC GW
75, 000 kg
Mach
0.80
TAS
479 kt
GS
364 kt
FF
4, 544 kg/hr
SGR
12. 485 kg/gnm
FBO required
1, 900 kg
152 gnm
FL310 wind/temp
115 kt/ISA +10
Initial
climb
Auckland
150
Copyright Avfacts 1998.
Step climb calcs page 2.
Working:
Step 2. Add step climb fuel
@ 50 kg/1, 000 ft to get start climb GW.
Step 1. Refer page 2-14 to find maximum arrival GW
at FL350/Mach 0.80.
Flight Level
Crz Schedule
ISA +10
350
M 0.80
72, 900 kg
72, 900 + 200 kg = Start climb GW of
73, 100 kg.
Step 3. Subtract start climb GW from
current GW to get FBO required.
75, 000 - 73, 100 kg = 1, 900 kg.
Step 5. Fill in flight profile to get SGR as normal.
Divide FBO required by the SGR to get distance to
the start of the step climb.
1, 900 kg
12.845
Step 4. Find EMZW by adding step
climb GW and current GW together,
then dividing by two.
75, 000 kg + 73, 100 kg
2
= 74, 050 (say 74T)
=152 gnm past TopC Answer !
Points to note:
•
•
•
•
A common mistake is to subtract the step climb fuel from the TopC GW instead of adding it. This will
almost definately mean a fail in this case.
Be aware of whether it is a head or tail wind. Another way to fail.
When finding the TopC GW at the new level, remember to use the ISA deviation/Mach number
combination at the new level.
If you are asked to step climb as soon as possible, and no cruise Mach number for the new level is quoted,
enter page 2-14 and extract the cruise schedule that has the highest GW. This will reduce the fuel burn off
required, and in doing so shorten the distance to the start of climb point. Typically M 0.79 will allow a
Example 2.
A B727 is tracking from Auckland (New Zealand) to Brisbane on ERC H5 route A464.
Position at 1243 UTC is waypoint “ISROB”, which is 200 DME Auckland, on the 279 Auckland omni radial,
FL310. Cruise schedule is Mach 0.82 at a gross weight of 72, 000 kg. Wind/temp 270M/70 kt/ISA +15.
A “light chop” is being experienced which is delaying the cabin food service. The Captain wishes to climb
into the smooth air reported at FL350 as soon as possible.
Assuming the aircraft continues at Mach 0.82/FL310 until a climb to FL350 can be commenced, and that
Mach 0.82 schedule will be used on reaching FL350 where the temperature is ISA +15, at what minimum
distance past “ISROB” can the climb to FL350 be commenced ?
Refer to next page for flight profile and working.
Copyright Avfacts 1998.
FL350 ISA +15
Step climb calcs page 3.
67, 700 kg
To Brisbane
Mach 0.82
67, 900 kg
“ISROB”
72, 000 kg
EMZW
70
200 kg
Step climb fuel
Mach
0.82
TAS
496 kt
GS
426 kt
FF
4, 653 kg/hr
SGR
10.922 kg/gnm
FBO required
4, 100 kg
Start of
step climb
FL310
70 kt/ISA +15
Trk 273M/375 gnm
Auckland
200 gnm
Flight profile
Step 2. Add step climb fuel
@ 50 kg/1, 000 ft to get start climb GW.
Working:
Step 1. Refer page 2-14 to find maximum arrival GW
at FL350/Mach 0.82.
Flight Level
Crz Schedule
ISA +15
350
M 0.82
67, 700 kg
67, 700 + 200 kg = Start climb GW of
67, 900 kg.
Step 3. Subtract start climb GW from
current GW to get FBO required.
72, 000 - 67, 900 kg = 4, 100 kg.
Step 5. Fill in flight profile to get SGR as normal.
Divide FBO required by the SGR to get distance to
the start of the step climb.
Step 4. Find EMZW by adding step
climb GW and current GW together,
then dividing by two.
67, 900 kg + 72, 000 kg
2
= 69, 950 (say 70T)
4, 100 kg
10.922
= 375 gnm past “ISROB” Answer !
Point to note:
•
A good idea would have been to accept a reduced Mach number cruise schedule at FL350 (say M 0.79).
This would mean you could have climbed earlier ( approx 46 gnm past TopC).
Copyright Avfacts 1998.
Step climb calcs page 4.
Example 3.
A B727 is tracking from Sydney to Auckland (New Zealand) on ERC H5 route L521.
Position at 1202 UTC is waypoint “ANULI”, which is 200 DME Sydney, on the 102 Sydney omni radial.
Cruise sched: M 0.84/FL330.
Current OAT -55C.
GW 72, 800 kg.
TWC 35 kt.
The Captain wishes to climb the aircraft to FL370 as soon as possible to take advantage of a significant
increase in TWC at that level. To allow the step climb sooner, the Captain has accepted the lower cruise
schedule of M 0.79 at FL370.
Assuming the aircraft continues at Mach 0.84/FL330 until a climb to FL370 can be commenced, and that
Mach 0.79 schedule will be used on reaching FL370 where the temperature is ISA, at what time can the climb
to FL370 be commenced in the current conditions?
69, 900 kg
1202 UTC
“ANULI”
35 kt/ISA -5
EMZW
71
ISA
M 0.79
200 kg
FL330
GW 72, 800 kg
Sydney
200 gnm
Mach
0.84
TAS
483 kt
GS
518 kt
FF
4, 578 kg/hr
SGR
8.838 kg/gnm
FBO required
2, 700 kg
Start climb 70, 100 kg/1237.3 UTC
35.3 min/305 gnm
Flight profile
Working:
Step 2. Add step climb fuel
@ 50 kg/1, 000 ft to get start climb GW.
Step 1. Refer page 2-14 to find maximum arrival GW
at FL370/Mach 0.79.
Flight Level
Crz Schedule
ISA
370
M 0.79
69, 900 kg
69, 900 + 200 kg = Start climb GW of
70, 100 kg.
Step 3. Subtract start climb GW from
current GW to get FBO required.
Step 5. Fill in flight profile to get SGR as normal.
Step 6. Divide FBO required by the SGR to get
distance to the start of the step climb.
2, 700 kg
8.838
= 305 gnm past “ANULI” Answer !
72, 800 - 70, 100 kg = 2, 700 kg.
Step 4. Find EMZW by adding step
climb GW and current GW together,
then dividing by two.
70, 100 kg + 72, 800 kg
2
= 71, 450 (say 71T)
Step 7. With GS of 518 kt, ETA at step climb is 1237.3 UTC.
Now try the step climb assignments.