I was recently looking at the approach to RWY 8L at Honolulu, Hawaii (PHNL).

Looking at the approach IAFs, I see the LOC RWY 8L approach has many different options, and has an intercept altitude at 2,300 ft. The ILS RWY 8L approach has three IAFs but none are south of the airport, and the glide slope intercept altitude is 2,700 ft.

In the scenario where a visual approach isn't appropriate and an ILS may be necessary, are there procedures/rules in place for a pilot to transition from the LOC approach to the ILS with glide slope once they are lined up? I know the LOC intercept is at a lower altitude, so can a pilot just intercept the glide slope from that altitude or are the two procedures incompatible and radar vectors are required to line the pilot up for the ILS?

I'm looking specifically at the JULLE5 STAR into the LOC 8L approach. JULLE5 ends at ALANA. The LOC has a IAF from ALANA, while the ILS doesn't (only BOOKE).

  • $\begingroup$ I don't understand your question. Transitions? The ILS has and the LOC each have three Initial Approach Fixes (IAF) to transition to the approach from the enroute environment. Levels? The ILS will get you down as low as 200' above the Touchdown Zone Elevation (TDZE), whereas the LOC will get you no lower than 500' above TDZE. $\endgroup$ – J Walters Dec 27 '16 at 19:42
  • $\begingroup$ In actual practice ATC will vector arriving aircraft onto the ILS. In the case of a radar outage, most arriving aircraft will have RNAV capability and can transition from the arrival to the ILS approach via any of the three IAF, as applicable. $\endgroup$ – J Walters Dec 27 '16 at 19:50
  • $\begingroup$ If you want to discuss this further you could explain your question in chat. $\endgroup$ – J Walters Dec 27 '16 at 19:52
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    $\begingroup$ Note that the JULLE FIVE STAR chart says "Expect vectors to final approach course". So if you fly ILS RWY 8L, the controller apparently has to tell you how to get from ALANA to one SELIC or MAKOA, the IAFs. $\endgroup$ – Jan Hudec Dec 27 '16 at 20:31
  • $\begingroup$ @JonathanWalters yes you are correct, I read the chart and wrote the post last night, but didn't post it until this morning and didn't catch my error. Thanks! I've updated the question. $\endgroup$ – lightbord Dec 28 '16 at 4:02

You can't legally switch from the LOC to ILS approach without ATC approval in this case, since they are different enough and are on different plates. However, if you're outside the FAF you can ask ATC to switch from LOC to ILS, and proceed with the ILS if approved. However, in lost comms, if you got initial approval for the LOC approach but no mentions of ILS, you can't switch to the ILS. Unless you exercise your emergency authority.


If you read the STAR, once you reach ALANA, fix, you can expect radar vectors to final approach course and clearance to fly the ILS RWY 8L. Most likely Honolulu approach will give you vectors southwest of PHNL to southwest of MAKOA fix, then instruct you to turn right to a northeast heading to intercept the localizer and give you approach clearance. Once you get clearance to fly the approach and acquire the localizer, you are committed to flying an ILS approach, as there are no optional LOC stepdown fixes published on this plate. This makes the PHNL ILS RWY 8L approach rather unique as most ILS approach plates list LOC stepdown fixes and a MAP along with them. There, the option to fly either the ILS to published DA or just fly the LOC approach to publiched MDA and MAP is up to the discretion of the pilot. Generally speaking, most aircrews will opt for the precision ILS rather than ignoring the glideslope and flying the nonprecision localizer approach. But that's your call as a pilot.


For the first part of your question you need to understand the parts of an ILS. ILS stands for Instrument Landing System.

The ILS system may be divided functionally into three parts: (a) Guidance information: localizer, glide slope; (b) Range information: marker beacon, DME; and (c) Visual information: approach lights, touchdown and centerline lights, runway lights

The localizer provides horizontal guidance. The glide slope provides vertical guidance, and the DME and marker beacons provide distance guidance. Notice the straight-in minimums on the ILS RWY 8L approach chart. They are 213-½ which means that an aircraft can fly down the glideslope until it is 200' above the ground. If they see the the approach light system (which in this case is a MALSR) they can proceed another 100'. If they don’t see the runway at 100' above the runway then they need to fly a missed approach.

There is actually a list of things they need to see in order to continue the approach—runway end identifier lights (REIL, the flashing strobes on either side of the threshold) the runway (itself, the markings, or lights) the threshold (itself, the markings, or lights) visual glideslopes (VASI, PAPI, etc.) the touchdown zone (itself, the markings, or lights)

The localizer approach uses the same horizontal guidance as the ILS but it does not provide vertical guidance. Notice that the straight-in minimums are 460'. That’s because the pilot is relying solely on the altimeter for vertical guidance and it is not as accurate as the glide slope.

Both approaches use the outer marker. The ILS uses it as a way to verify that the aircraft is at 1994' when it crosses the marker. The Localizer approach uses it as a step-down fix—the aircraft can begin its final descent to landing. In this approach the pilot must not descend below 2000' unless the items above are seen. At 0 DME they begin the missed approach.

Most aircraft that are equipped with IFR instruments will have a glideslope. However, it may be inoperative or the glideslope at the airport may be inoperative in which case they would fly the localizer approach.

I don’t know if they do it at this airport, but often airports with two parallel runways will use the localizer approach to one runway with a side-step to the other. If ceilings are high enough, they may do it here.

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    $\begingroup$ This is a nice description of ILS, but I am pretty sure OP understands all of this and it is absolutely irrelevant to the question, which is not about minima and missed approach, but instead about why the initial approach fixes differ (look at the linked charts!), whether the segment from one approach can be used to get to the IAF of the other when the STAR does not lead all the way there, or what can be used instead. $\endgroup$ – Jan Hudec Dec 27 '16 at 20:22
  • $\begingroup$ @JanHudec bingo, thanks for clarifying my words better than I could! $\endgroup$ – lightbord Dec 28 '16 at 1:33
  • $\begingroup$ Sorry about the confusion. I’m still having trouble understanding questions when the OP is not a native speaker. $\endgroup$ – JScarry Dec 30 '16 at 21:12
  • $\begingroup$ This is a good answer which was initially provided to the original question which was fairly incomprehensible and seemed to display a significant lack of understanding of the ILS. $\endgroup$ – J Walters Jan 18 '17 at 23:25

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