I'm seeing this same problem with the CS 757 freighter at KSDF. In a Worldport position, the loader approaches, gets near the top of its travel, and Couatl blows up with the same walker.py error that was referenced above.
From my log:
Warped to UPS Worldport Ramp 1|Cargo Stand D2
Slew mode True
Slew mode False
Requested assistance services at UPS Worldport Ramp 1|Cargo Stand D2
Error: no model for Couatl type Staircase available for ICAO KSDF and params {'isCargoStand': True, 'isCargo': True, 'exitAlt': 4.021639216517383, 'parkingRadius': 34.75}
Total payload:0 lbs.
Estimated number of passengers = 1
Traceback (most recent call last):
File ".\common\walker.py", line 317, in _walkToAsync
File ".\common\walker.py", line 271, in _walkTo
IndexError: tuple index out of range
{'Airport': 'KSDF', 'Requested assistance services at': 'UPS Worldport Ramp 1|Cargo Stand D2', 'User Pos': (38.17633092807564, -85.74132815764337, 156.044 m, 3.24736 m, 153.0986832303669)}
The loading seems to be fine at a non-Worldport postion on the Fedex ramp at KSDF.
Regards
Bob Scott