You can find all sort of interesting things on approach plates. Take the ILS 17L into Colorado Springs (KCOS). The approach is a standard Category I ILS, yet the minimums block contains some non-standard minimums:
What’s that “RA 169” all about?
RA in this case stands for radar altimeter; the decision to go-around or land is made referenced to height above ground, not a baro-altimeter setting. Most modern light jets equipped with radar altimeters have a means of selecting “Baro” or “Radar” minimums to be entered into the PFD, triggering the “minimums” alert. Looking at notes 1 and 2, though, it’s apparent that not everyone can use a radar altitiude of 169’ as DH. The big limit is the note that use of a heads-up display, or HUD, is required. Even aircraft equipped with a HUD aren’t automatically able to drop an extra 50’; the flight crew and aircraft must have been granted authority via an LOA, as well.
The requirements to be granted the LOA are spelled out by the FAA in order 8400.13D, which specifies the crew and aircraft must be certified for Category II operations. Additionally, single pilot operations are specifically prohibited from using the lower minimums.
So while it’s apparent the average owner –flown light jet won’t be able to fly Cat I ILSs to 150’ minimums anytime soon, what is of interest is the trend approaches like this represent. “Special Authorization (SA)” procedures are becoming more common, with required navigation performance (RNP) approaches, being the main example. Rather than a one-size fits all mentality to airspace management, the FAA is shifting to a “best equipped, best served” philosophy. Operators with the requisite toys will be authorized to fly approaches others can’t, or to fly a standard approach to lower minimums.
And while it will likely be some time before light jets are delivered with HUD units, the next SA ILS authorization being studied will utilize a technology already available- synthetic vision (SV). As envisioned, aircraft with a radar altimeter, WAAS, and SV will also be able to take advantage of 150’ DHs. Pilot and aircraft certification will still be required, and it’s not certain if single pilot operations will be permitted.
