Let's take ILS, for example.

As stated in the FARs, the minimum RVR for a CAT I ILS approach would be 2400ft (1/2 SM) for a runway that does not have TDZ and Centerline Lighting. So, that is one limitation for such a scenario.

A couple more would be the limitation to the visual references available under 91.175 of the FARs.

Can you think of any other disadvantages if one were to conduct a precision approach on a non-precision runway?


1 Answer 1


Your limitations are exactly the same regardless of runway -- you cannot descend below the published DH without the published flight visibility minimum and the visual references required by 91.175.

What the limited runway markings and lights change is the number of visual cues you have to be able to descend below MDA and land, which affects the likelihood of a successful approach in minimum weather. Whether this is a disadvantage or not depends on the actual weather and your preparation. If you know what lighting and markings are available (and you should), then you know what to look for. If you are looking for lights that don't exist, you won't find them and worst case you may mis-identify other lights.

The only other disadvantages I can think of relate to ground movement and ILS critical area protection. If there are no centerline lights on the runway there probably aren't lighted runway turnoff lead lines either and extra care needs to be taken when taxiing. If the runway is located at an non-towered field and the ILS critical area has a hold short line on the taxi way, it may not be protected properly. This is mitigated, however, by taxiway placement which probably avoids the critical area at non-towered fields (not universally true though).

  • $\begingroup$ So basically what you're saying is, if you can see X you may descend; if an airport doesn't have X you can't possibly see it, and if you do, you're at the wrong airport, or looking at the wrong thing/wrong lights? That actually makes a bunch of sense logically. :) $\endgroup$
    – falstro
    Commented Sep 15, 2015 at 8:34
  • $\begingroup$ How often do non-towered airports have ILS? Or should I ask a new question... $\endgroup$
    – FreeMan
    Commented Sep 15, 2015 at 12:40
  • 2
    $\begingroup$ @FreeMan aviation.stackexchange.com/questions/5163/… and there is also the more common situation that the ILS is at a part time tower and they'll leave it on (for one of the runways) overnight when the tower is closed. $\endgroup$
    – casey
    Commented Sep 15, 2015 at 13:22
  • $\begingroup$ Thanks, @casey. Totally contradictory to the sense that's common in my head, but that's why I'm here - to learn. $\endgroup$
    – FreeMan
    Commented Sep 15, 2015 at 13:53

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