Canuck
David Megginson
- Joined
- Mar 31, 2016
- Messages
- 7,085
- Reaction score
- 3,903
While I was practicing approaches this morning, I ended up with an ILS and then an RNAV (LPV) approach to the same runway, so I thought it would be interesting to compare the tracks. I'm using an STEC-20 (rate-based) single-axis autopilot, and there was light chop and thermal activity.
The first approach is the CYOW ILS 32 — I approach from the east on vectors with the autopilot in heading mode, then switch to HI (Nav) mode once I've intercepted the inbound. As you can see in the screencap below, there's some mild scalloping (which showed up as ± half a dot on my CDI) at first while the STEC-20 adjusts to the crosswind, then from that point on, it's tracking the localiser precisely with a 10° crosswind correction all the way in (there's no more scalloping past the part I cropped).
The second approach is the CYOW RNAV 32 Z — I approach from the west on the base leg of the T, with the autopilot in GPSS mode, and the autopilot keeps me absolutely straight all the way in (that's the base line that the first one scallops around).
Make of it what you will. I see no reason to replace my old STEC-20 with a new, all-digital A/P until it fails on me some day, because it gets the job done.
The first approach is the CYOW ILS 32 — I approach from the east on vectors with the autopilot in heading mode, then switch to HI (Nav) mode once I've intercepted the inbound. As you can see in the screencap below, there's some mild scalloping (which showed up as ± half a dot on my CDI) at first while the STEC-20 adjusts to the crosswind, then from that point on, it's tracking the localiser precisely with a 10° crosswind correction all the way in (there's no more scalloping past the part I cropped).
The second approach is the CYOW RNAV 32 Z — I approach from the west on the base leg of the T, with the autopilot in GPSS mode, and the autopilot keeps me absolutely straight all the way in (that's the base line that the first one scallops around).
Make of it what you will. I see no reason to replace my old STEC-20 with a new, all-digital A/P until it fails on me some day, because it gets the job done.
