Learn PMDG Boeing IRS alignment, realistic wait times, FMC position entry, and fixes for flashing ALIGN lights on the 737, 747 and 777.
To align a PMDG Boeing IRS, supply stable electrical power, keep the aircraft stationary, select each IRS/IRU to NAV or switch the ADIRU on, and enter the present GPS position on the FMC/CDU POS INIT page. A realistic cold alignment normally takes about 7–10 minutes at ordinary latitudes; PMDG’s accelerated options are quicker.
PMDG IRS alignment procedure
Across PMDG Boeing products for Microsoft Flight Simulator, FSX and Prepar3D, the underlying sequence is the same, although the overhead controls differ by aircraft.
| PMDG aircraft | Alignment control |
|---|---|
| 737 | Set the left and right IRS mode selectors to NAV |
| 747 | Set all three IRS mode selectors to NAV |
| 777 | Switch the ADIRU on, then initialise its position through the CDU |
- Establish stable electrical power. Use external power, the APU or running-engine generators as appropriate. Set the parking brake and do not allow pushback to begin.
- Start the alignment. On the 737 and 747, move the selectors from
OFFdirectly toNAV; the units pass through alignment automatically. Leaving them inALIGNis a common mistake because they will not enter normal navigation mode there. - Open the FMC position page. Select
POS INITon the CDU. Enter the reference airport or gate if the product requests it, then locate the displayed GPS position. On some CDU versions, GPS L and GPS R appear on a subsequent POS INIT page. - Set the inertial position. Copy the displayed GPS coordinates into
SET IRS POSorSET INERTIAL POS. Use the aircraft’s actual location—not the destination, a stale last position or an approximate airport position. - Wait without moving. Do not taxi, push back, use slew mode or repeatedly turn the selectors. Any movement or reset can invalidate the alignment and restart the timer.
- Check completion. The ALIGN annunciators should extinguish, valid attitude and heading information should appear, and the FMC should stop requesting an inertial position.
For the exact 737 power-up order and CDU entries, follow our PMDG 737 cold-and-dark alignment sequence. Once the inertial systems are ready, continue with the 737 FMC route-programming process.
How long does PMDG IRS alignment take?
A full realistic PMDG IRS alignment usually takes about 7–10 minutes at normal operating latitudes, but latitude, aircraft type and the selected PMDG realism option affect the wait.
| Alignment setting or state | Expected wait |
|---|---|
| Realistic cold alignment | Usually 7–10 minutes at mid-latitudes; it can take longer at high latitudes |
| Accelerated or short alignment | Seconds to a few minutes, depending on the PMDG product and option |
| Instant alignment | Almost immediate after power and valid position entry |
| Saved state with IRS already aligned | No full wait unless the state has reset or the position is invalid |
The option names and locations vary. Older products commonly place them in PMDG Setup pages on the CDU, while newer aircraft may use an electronic flight bag or aircraft-options menu. Route distance has no bearing on alignment time.
Why is the PMDG ALIGN light flashing?
A flashing ALIGN light usually means the IRS cannot complete alignment because its position is missing or unacceptable, or because the aircraft moved during the process. A steady ALIGN light normally means the timer is still running.
- No inertial position entered: copy the GPS position into the relevant SET IRS POS field.
- Incorrect coordinates: check for a large difference between the entered position and the GPS or loaded gate position.
- Aircraft movement: stop the aircraft completely and perform a fresh alignment.
- Interrupted electrical power: restore stable AC power before restarting the units.
- Wrong selector position: make sure 737 and 747 selectors finish in
NAV, notALIGN. - Conflicting controls or failures: check for hardware bindings that keep commanding an IRS selector and inspect PMDG’s failure settings if a FAULT light appears.
For a clean reset, stop the aircraft, set the selectors to OFF, wait until their shutdown cycle and lights have finished, restore stable power, select NAV or ADIRU ON, and enter the GPS position again. Repeatedly rotating the selectors only restarts the process.
Can I push back while the IRS is aligning?
No—complete a full cold IRS alignment before pushback or taxi. Once the ALIGN lights are out and valid attitude and heading are displayed, the aircraft can move without cancelling the alignment.
If the IRS is aligned but LNAV or VNAV still refuses to engage, the next likely causes are an inactive route, missing performance data or unsuitable engagement conditions; use our 737 LNAV and VNAV troubleshooting checks rather than resetting the IRS again.