iFly 747 in FSX: FMC shows insufficient fuel and ZFW/GW manual entry invalid

Fuel message + ZFW/GW “INVALID ENTRY” on the iFly 747

A couple of things are getting mixed together here: (1) how the iFly FMC is calculating “fuel required” for the route, and (2) what the FMC will/won’t let you type into the weight fields.

1) “INSUFFICIENT FUEL” even though you loaded plenty
On the 747 (and most Boeings), that message is usually based on the FMC’s predicted fuel at destination versus the reserves you’ve told it to carry (plus whatever performance/route data it has). If the FMC doesn’t have the route/forecast/perf side filled in yet, it can give you a low/incorrect prediction and throw the message.

Try this order for a quick test flight:

1. In FSX, load fuel normally (what you did is fine for a test). Don’t worry too much about “tank order” for a simple KLAX-KSEA hop.
2. In the FMC, make sure you have a complete route in (origin/dest + legs).
3. Go to the PERF INIT / INIT pages and make sure you enter reserves (and cost index if it asks). If “RESERVES” is huge or set wrong, it’ll trigger the insufficient fuel message even with a lot onboard.
4. Verify the fuel on board the FMC “sees” matches what you loaded in FSX (it should show total fuel reasonably close to your 65.9k).

If after you’ve got the route and PERF INIT filled out it still says insufficient, then it’s usually a mismatch between what FSX loaded and what the iFly is reading (or the units are confusing you).

Tank loading
For short flights with relatively low fuel, you generally want fuel in the mains before you start stuffing aux/center, but the bigger issue here is simply making sure the FMC is getting the correct total fuel value and you’ve set a sensible reserve. The “evenly between left and right tanks” part is fine as long as the airplane’s tanks you’re editing are actually the mains and not something odd in the FSX fuel screen mapping.

2) ZFW / Gross Weight manual entry gives “INVALID ENTRY”
On these Boeings you typically don’t type a random ZFW/GW into the scratchpad and overwrite it unless the FMC is designed to accept it. Many add-ons want you to set payload in the sim/loader, and then on the FMC you only “confirm” it (or it’s auto-filled and you can only enter ZFW in a very specific format on a specific line).

A few common gotchas that cause “INVALID ENTRY”:

• You’re trying to enter GW where the FMC expects ZFW (or vice-versa).
• Wrong format (some expect no commas/decimals, some expect “/” entries, etc.).
• Units mismatch (even if you converted, the FMC may still be set to LBS internally, or it’s expecting a different unit than you think).
• The field isn’t actually editable on that page in this model until weights are set via payload/fuel first.

What I’d do next

1. Set payload and fuel in the FSX Fuel/Payload screen first.
2. Then go into the FMC and look for the page where it shows ZFW and allows a “set”/“confirm” style entry (often you copy the displayed value into the scratchpad and line-select it back, depending on the add-on).
3. Only after that, complete PERF INIT (including reserves) and see if the insufficient fuel message clears.

A couple quick questions so we can pin it down

• Which exact iFly 747 package is this (the iFly 747-400 for FSX, or another variant) and does it include a separate fuel/payload loader?
• When the FMC says “INSUFFICIENT FUEL,” what are your RESERVES set to (and what does the FMC predict for fuel at destination)?
• On the FMC page where you’re trying to enter ZFW/GW, what exactly are you typing (example value and whether it’s on the ZFW line or GW line)?