A question about GPS approaches

[oneleg]

In an airport with several GPS approaches available as options, who selects the GPS approach and based on what?

[tiger1962]

I always select whichever approach is heading into the wind.

[PhrogPhlyer]

Generally, the approach (and any associated STAR) is based upon a) runway in use (aligned into the wind), and b) shortest routing to the IAF.

These minimize time in the air which saves fuel and keeps passengers happy.

 

Visualize a straight line from departure to destination airport, and select whatever arrival/approach takes you the least distance from that line (of course to land into the wind).

 

[oneleg]

Thanks, but who decides?  I'm thinking each approach has to be assigned to each plane in a towered airport because the ATC has the best knowledge of where the other incoming planes are at any given moment and can give specific instructions to avoid a collision between two incoming planes.  BUT, that doesn't seem to be the case in reading transmission transcripts between the pilot and ATC. There are examples here:

VFR Radio Communications Script for All Scenarios (flight-insight.com)

In the above examples, I don't see the pilot letting the ATC know which approach he is taking and neither am I seeing the ATC giving instructions to which approach the pilot is taking. Isn't the pilot required to ask permission for a given approach before actually doing so?

Also, can a pilot change his or her mind between the IAF and FAF ie. decides on a precision approach but somewhere on final approach decides to do a non-precision approach instead (eg. change from VFR to IFR)? 

[flightstrike]

Hi Oneleg,

 

This can become a complicated subject, but here's a "simplistic" description.

 

If the Airfield is "Controlled" i.e. ATC. Then it's generally up to the controllers to dictate which Arrival (STAR) and which Approach will be used. Variables such as Weather (most into wind RWY), Traffic (density and what direction are they all coming from) will further dictate which procedures ATC use. Yes, Pilots can "require" a particular Approach if they need to (maybe the into wind RWY is too short, or too much tail wind etc), but generally speaking, we will accept the Arrival and Approach assigned to us by ATC.

 

Can you change your mind? You can to a certain degree. If you've been cleared for a particular approach, then ATC expect you to track a particular way (route) and at certain speeds. This is to separate you from other Aircraft. If there's a particular change you wish to make, such as cut a corner or change to visual approach, this needs to be requested and approved by ATC. It's not uncommon to have everyone on an Instrument Approach in good weather, for no other purpose than to have everyone spaced out a certain distance, and at expected speeds. If everyone was just "cleared visual approach" speed constraints can be waived and separation between aircraft could be reduced to unacceptable levels (from the point of view of ATC).

 

If the airfield isn't controlled. Then it might be as simple as the Pilot making a decision as they get closer to the field. Good weather, lets do a Visual Approach. Bad weather (or maybe some traffic), it might be best to conduct an Instrument approach. In which case, our procedures dictate that we pick a "straight in" approach where possible. As opposed to an approach that requires us to fly over an Aid like a VOR or NDB. This saves time and fuel.

However, the airport may have written procedures that dictate how Aircraft approach and depart the particular airfield. This may be due to the density of traffic, terrain, local noise abatement requirements etc.

 

I hope this helps.

[oneleg]

13 hours ago, flightstrike said:

 

This can become a complicated subject, but here's a "simplistic" description.

 

If the Airfield is "Controlled" i.e. ATC. Then it's generally up to the controllers to dictate which Arrival (STAR) and which Approach will be used. Variables such as Weather (most into wind RWY), Traffic (density and what direction are they all coming from) will further dictate which procedures ATC use. Yes, Pilots can "require" a particular Approach if they need to (maybe the into wind RWY is too short, or too much tail wind etc), but generally speaking, we will accept the Arrival and Approach assigned to us by ATC.

 

Can you change your mind? You can to a certain degree. If you've been cleared for a particular approach, then ATC expect you to track a particular way (route) and at certain speeds. This is to 

@flightstrike This was very helpful. Thank you for taking the time to reply. Very much appreciated. A couple of follow-up questions if I may:

1. In the sample transcripts above between ATC and the pilot, I don't see ATC assigning a specific approach to the pilot. Are these sample transcripts wrong or missing some things? Are all ATC communications with the pilot recorded? What are the ramifications if either party commits an error?

2. Does ATC name a specific precision or non-precision approach type, for the pilot to take eg. LNAV, LNAV/VNAV, LPV, etc.  Put another way, how does the ATC know what approach is available to the pilot eg. what kind of avionics devices are installed in the plane?
 

[nsproles]

I believe that it is up to the pilot to request a specific type of approach and it is up to ATC to approve or otherwise.  This URL describes the procedure in the USA;

https://www.faa.gov/air_traffic/publications/atpubs/atc_html/chap4_section_8.html

 

On reading this publication, the logic of both the pilot and  ATC knowing the type of approach being attempted, allows ATC to update the pilot on  any changes that may affect the approach e.g. glideslope equipment failing or runway visual range changes.

 

After watching analyses of aircraft crashes on YouTube, it would appear that ATC does record communications with aircraft.  Whether this applies for all jurisdictions, I do not know.

 

[oneleg]

3 hours ago, nsproles said:

 

After watching analyses of aircraft crashes on YouTube, it would appear that ATC does record communications with aircraft.  Whether this applies for all jurisdictions, I do not know.

 

I was just watching this on YouTube!