"I have no clue what she just said" - IFR Student attempting to read back a clearance
The Segments of an Approach
The instrument approach procedure (IAP) is traditionally composed of three segments:
Initial approach segment, which is from the initial approach fix (IAF) to the intermediate fix (IF). The purpose of the initial segment is to guide you to the final approach course (FAC), which gets you aligned with the runway (or at the very least to the final path to the runway). An approach can have multiple IAFs, to facilitate arrivals from multiple directions. A great example is the RNAV "T" approaches as shown in the image below. There are cases where the IAF is also an IF. This is very common when you have a hold in lieu of a procedure turn. In this case, you can argue that the initial approach segment is the procedure turn that allows you to turn inbound and aligned on the FAC.
Intermediate approach segment, which is from the IF to the final approach fix (FAF). Historically, this segment is designed to allow aircraft to configure for landing (e.g., flaps, gear) on a straight segment.
Final approach segment, which is from the FAF to your missed approach point (MAP) (or Decision Altitude [DA]). This is the heart of the approach. In the case of an approach with vertical guidance (APV) or an ILS, you will typically capture the glideslope on that segment. There are slight exceptions concerning a precision FAF (PFAF), but that's a conversation for another time.
Clearances
Approaches are historically designed to be flown "in full" from the IAF. With changing times, newer airplanes and newer procedures that is no longer always the case. Nevertheless, a pilot should expect to be either cleared to teh IAF or IF, or via vectors. A clearance can be issued if the aircraft is on a published segment of the approach or with a minimum safe altitude based on various factors, inclusing minimum vectoring altitude (MVA).
Cleared to an IAF or IF
When you are cleared direct to an IAF, you can descend to the specified altitude and begin the approach without further instructions. If an IAF does not exist, you can expect a clearance to an IF. In the case of the plate above, you can expect a clearance like "Cross WOXIT at or above 2,500, cleared RNAV 28 approach".
Terminal Arrival Areas (TAA)
There is an exception around which there is a lot of confusion, and this is the Terminal Arrival Area (TAA). The purpose of the TAA is to allow for ATC to clear you for an approach without specifying an altitude. That is because the TAA provides you with a protection altitude. As you've noticed in the previous paragraph, ATC provided a crossing altitude. If you do not receive one, you should look for the TAA. In the image below, assume you are the blue arrow, flying from the east direct TELOE. ATC can remove the altitude restriction and just say: "Proceed direct WOXIT, cleared RNAV 28 approach". In that case, you can descent to 2,500 ft as depicted on the TAA illustration below, as long as you're within 30 NM of TELOE. The odds of being cleared that far out are rather small, but in theory you could maintain your assigned altitude until reaching 30 NM and then descend to 2,500 ft.
Cleared to a FAF which is also an IAF
ATC cannot clear you directly to a FAF. The only exception is if the FAF is also an IAF. This is often found in a case where you can reach the FAF from the opposite direction and fly outbound for a procedure turn. In the case of the ILS below, I can be vectored direct ONYUN, but only if I fly the localizer backwards to execute the procedure turn as depicted. This is further reference in JO 7110.65W paragraph 4-8-1 (c) (that's the ATC manual).
Cleared Vectors to Final
Vectors to final are among the most common method of executing an approach. The reason for that is that they may shorten the approach significantly and help ATC sequence traffic. Vectors to final means that ATC will provide you with headings to intercept the FAC. There are, however, some rules. The airplane needs to intercept the FAC at least 2 NM prior to the approach gate to give time to the pilot to configure and stabilize on the FAC. This gate is an imaginary point on the FAC that lives between 1 and 5 NM prior to the FAF. It's existence is dictated by the requirement of of having the gate be > 5 NM from the runway threshold. Typically the FAF will be at 5 NM, which means you will get a vector 3 NM out (FAF is 5 NM out, so gate will be +1 NM, and minimum distance from vector is +2 NM. So 1+2 = 3 NM out). The most common clearance will use the "until established" verbiage, to highlight that upon being issued a clearance, ATC expects you to capture the FAC on your own.
For example,
"Turn left heading 130, maintain 2,000 until established, cleared ILS 10 approach"
ATC might also indicate your distance from the FAF,
"Cherokee 73N, 5 miles from SOVIE, turn left heading 130, maintain 2,000 until established, cleared ILS 10 approach"
There is also the case in which if you are likely to not be capturing the FAC easily (say you are far from the service volume of the localizer), ATC can invite you to "report established". In that case, once you report established, you will be issued a full clearance.
Legal Phraseology
As a reminder, ATC needs to hear the full clearance readback for the voice recorded in case something goes wrong. As a CFII, I very often will repeat the entire clerance if my student missed something. ATC knows us well as training aircraft, and they may not say something cause they know a CFI is on board. But nevertheless, I'll repeat it and add "for the tapes".
NOTE: The article wasre reviewed for accuracy by an experienced ATC controller at KNBC.
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