Airbus MCDU Radio Navigation (RAD NAV) & INIT B Fuel/Weight Entry
With the flight plan built, two setup pages remain before you're ready to fly: RAD NAV, where you tune your navigation aids, and INIT B, where you enter the aircraft's weight and fuel. This guide covers both, with the exact fields and example values you need.
1. Setting up RAD NAV
The RAD NAV page is where you set the frequencies for your key navigation aids. Press the RAD NAV button on the MCDU. The page is usually blank at first, though in some scenarios the frequency fields come pre-filled.
The navigation aids you'll work with are:
ILS — Instrument Landing System
VOR + DME — VHF Omnidirectional Range + Distance Measuring Equipment
ADF — Automatic Direction Finder
MLS — Microwave Landing System
These aids use identifiers (idents) that sometimes look like an airport's IATA code but are technically different. You can enter a frequency, an ident, or both. In our example we tune CTU VOR DME at 115.70 MHz.
24°); for a VOR, it's the radial you want to fly. For ADF entries, you don't need to enter a course at all.
2. Getting to the INIT B page
Go back to the MCDU's INIT page. The pagination arrows (← →) tell you there's a second screen — that's INIT B, the Fuel and Weight page.
3. Zero Fuel Weight & ZFWCG
The two fields to set first are Zero Fuel Weight (ZFW) and Zero Fuel Weight Center of Gravity (ZFWCG). Units depend on how the aircraft is configured — metric (tonnes / metres) or imperial (pounds / feet / gallons). Some MCDU modules display weights in thousands of pounds. A typical entry looks like 110.2 / 18.8 — 110,200 lb at 18.8% MAC.
Understanding ZFWCG
Center of gravity is the aircraft's balance point, expressed as a percentage of the wing's mean aerodynamic chord (MAC). The normal operating range is roughly 20–40% MAC: above 25% is aft, below 25% is forward. Stray outside the safe envelope and handling and safety degrade sharply. For a sim flight, assuming 25% is a reasonable default when you don't have a proper load-and-balance calculator.
4. BLOCK fuel & the fuel fields
Block fuel is the total fuel on board before pushback — trip fuel, contingency, alternate, final reserve, and taxi fuel all combined.
A quick way to estimate it: assume maximum burn at full engine power for the whole flight. An A320 burns roughly 5–6 tonnes per hour at full power, so for a short 190 nm route, under 10 tonnes is normally plenty.
Check FOB (Fuel On Board) on DU1, convert to tonnes, and enter it. On MCDU modules that auto-calculate, press R3 then R2 — this needs the engines fully started, and the exact key positions vary by MCDU version.
The fuel fields at a glance
| Field | What it is |
|---|---|
| TAXI | Taxi fuel — roughly 0.2–0.4 (thousand lb). Burned before takeoff. |
| TRIP/TIME | Trip fuel and time — auto-calculated; the crew can't change it. |
| RTE RSV/% | Route reserve — enter one value (fuel or %) and the other fills in automatically. |
| ALTN/TIME | Alternate diversion fuel and time — auto-calculated. |
| FINAL/TIME | Final reserve / holding time — entered by the crew. |
| EXTRA/TIME | Extra holding fuel at destination/alternate — auto-calculated. |
| TOW | Take-off weight. |
| LW | Landing weight. |
With RAD NAV tuned and INIT B complete, your Airbus knows how it's loaded and how far it can go — the pre-flight FMS setup is done.
Do it on real hardware.
Tune frequencies and dial in fuel on a backlit Rowsfire panel instead of a mouse — tactile keys, authentic Airbus layout, plug-and-play with MSFS & X-Plane.
Explore Rowsfire cockpit panels
