Pre-Flight Fuel Planning (PERF INIT)
PremiumintermediateAt the gate with the OFP for a Geneva sector: weights and fuel on PERF INIT, on one page where the Airbus uses two.
What this scenario covers
PERF INIT collects zero fuel weight, fuel on board, reserves, cost index and cruise altitude, and computes gross weight from them. From that the FMC produces every prediction it will make for the rest of the flight.
Boeing consolidates onto this single page what Airbus splits between INIT A and INIT B — a small difference that changes the shape of the crew flow more than it changes the data.
How it applies in flight ops
The numbers come from the loadsheet and the OFP, and they are entered once and cross-checked. Gross weight is the input that everything else scales from: get it wrong and the FMC will confidently predict the wrong fuel, the wrong times and the wrong optimum altitude.
Reserve fuel entered here is what the destination-fuel prediction is judged against later on PROGRESS, which is why an accurate entry at the gate is what makes the in-flight fuel check meaningful.
Fly this one with Premium
Everything about this scenario is on this page, steps included — reading it costs nothing and always will. What Premium adds is doing it: the CDU validates every entry as you make it, tells you when an entry was accepted but wrong, and saves your progress across devices.
Step-by-step: Pre-Flight Fuel Planning (PERF INIT)
- Open PERF INIT — the page that needs all the weight and fuel numbers from the OFP.
PERF INIT is Boeing's single fuel-and-weight setup page. The FMC needs ZFW, fuel, reserves and (optionally) cruise wind before it can compute trip fuel and predictions. Most carriers brief PERF INIT as part of the pre-flight scan.
- Enter Zero Fuel Weight 58.2 tonnes. Type 58.2 and press 3L.
Zero Fuel Weight = aircraft + crew + payload (passengers, baggage, cargo) but NO fuel. Comes from the loadsheet ground ops sends shortly before pushback. 58.2 t is typical for a 737-800 with ~165 passengers + 1.5 t baggage; a fuller flight could push 60+. Always check the loadsheet — wrong ZFW gives wrong V-speeds downstream.
- Enter Block Fuel uplift 6.0 tonnes. Type 6.0 and press 2L.
BLOCK fuel = trip + contingency + alternate + final reserve + taxi + any extra. For EGLL → LSGG (~480 nm), 6.0 t is realistic: 3.5 t trip + 0.2 contingency + 0.7 alternate (LFLY) + 1.0 final reserve + 0.2 taxi + 0.4 extra. The OFP shows the breakdown; you only enter the total.
- Enter Gross Weight 64.2 tonnes (ZFW + FUEL). Type 64.2 and press 1L.
Gross Weight is ZFW + total fuel. A real Boeing FMC computes GR WT automatically from the ZFW and FUEL you entered above; the trainer asks you to enter it explicitly so you understand what the FMC is doing. GR WT is the input to performance — V-speeds, climb gradients, OPT/MAX altitudes all depend on it.
- Enter Reserves 2.0 tonnes. Type 2.0 and press 4L.
Boeing combines route reserve + final reserve into one RESERVES field (vs. Airbus separating them on different LSKs). 2.0 t covers ~1.0 t final reserve (30-min hold at the alternate, ICAO/EASA mandate) + ~1.0 t route contingency for unforeseen events. The FMC uses this as a hard floor — if predicted arrival fuel falls below it, the page warns.
- Enter the average trip wind. Type 270/050 and press 2R.
CRZ WIND is the average wind component along your route, taken from the OFP's wind summary. 270/050 means 50 kt from the west — a strong westerly headwind for an eastbound EGLL → LSGG leg. The FMC uses this to refine its trip-fuel and ETA predictions; without it, predictions drift as actual winds differ from forecast.
- Set Cost Index 35. Type 35 and press 5L.
Cost index 35 is a typical short-haul value for the 737-800 — fast enough to hold the schedule, slow enough to save real fuel. Real OFPs print this value based on the day's fuel price vs crew/schedule costs. PERF INIT is the last pre-flight setup step before TAKEOFF REF.
What to take away
- PERF INIT is the 737's single weights-and-fuel page.
- ZFW and fuel come from the loadsheet and OFP; gross weight is computed.
- Every downstream prediction scales from these entries.
- The reserve you enter here is the yardstick for every later fuel check.
The rest of Performance & Fuel
TAKEOFF REF — V-speeds
PremiumintermediateTakeoff flap and V-speeds on the TAKEOFF REF page — the three numbers that turn a runway analysis into a takeoff you can fly.
📍 LEMD → EGLL⏱ ~3 min📊 6 stepsAssumed Temperature — Reduced Thrust Takeoff
PremiumbeginnerReduced-thrust takeoff, Boeing's way: the assumed temperature method. Tell the engines it is hotter than it is and they produce less thrust.
📍 LOWW → EDDM⏱ ~3 min📊 5 stepsCost Index — What Does It Do?
PremiumbeginnerThree cost index values on PERF INIT — 0, 30 and 80 — and the speed schedule changes under you.
📍 LIRF → LEMD⏱ ~3 min📊 5 stepsMid-Cruise Fuel Check (PROGRESS)
PremiumintermediateThirty minutes into the sector: read the predicted destination fuel on PROGRESS, then reconcile PERF INIT against what the gauges actually say.
📍 EGLL → LSGG — cruise FL360⏱ ~5 min📊 5 steps