Using the activate approach is fine if you are aware of how it works and it accomplishes what you want. In the US, we must be cleared for an approach which includes the instructions on how to join the approach. This may be by vectors to final, flying a feeder route to an IAF, or direct to an IAF. All of these may be accomplished with the activate approach. However, we can also be cleared direct to an IF or step down fix between the IF and the FAF. This may not be accomplished by using the activate function.
Although an airport may be located in class G airspace, all approaches are joined in some form of controlled airspace (E, D, C, or B). If an airport is located in class G airspace, only one IFR operation is permitted at a time, so there is no concept of entering class G airspace and then initiating an approach without ATC approval. Other points that tend to cause confusion is when an approach is activated on the redo or when a hold is required or not. The one that causes the most confusion is when a pilot is told they are being vectored for the approach, the pilot activates the approach using VTF, and then the controller clears the aircraft direct to a fix.
If an airport is located in class G airspace, only one IFR operation is permitted at a time, so there is no concept of entering class G airspace and then initiating an approach without ATC approval.
Obviously, there are some notable differences between what is possible to control at lower levels in the U.S. (where most of the “lower” States have radar coverage even at very low levels (see Atlas of Radar Coverage of Lower 48 CONUS Border States At 500’ and 1000’)) and Australia.
In Australia’s vast G-class airspace, where the universal carriage of ADS-B is still not mandated at present (see Australian airspace regulations ), “the very remote controller” usually can only provide one (flying under IFR) with “advisories” based on radio reports from other IFR traffic in one’s ops area (all IFR movements require continuous two-way communication to be established with the FS before entering IMC) and with “news” about any self-reported VFR traffic.
Thus, those of you, including those very few disgruntled Australian “expats”, who dare to accuse our Australian Government of over-controlling everything in its reach, are evidently grossly mistaken!
:no winkinking:
[edited with a new URL, on OP’s request]
However, we can also be cleared direct to an IF or step down fix between the IF and the FAF.
Getting cleared direct to an SDF is just amazing… that would confuse the hell out of anybody. How do you assess the descent profile (the MSA issue)?
Getting cleared direct to an SDF is just amazing… that would confuse the hell out of anybody. How do you assess the descent profile (the MSA issue)?
In the US, MSA has a different meaning than elsewhere. It is an altitude shown on most approach charts that provides terrain clearance of 1000 feet (2000 feet in mountainous areas) above the highest obstacle or terrain within a 25 NM radius around a specified location, a navaid for a conventional approach and the runway threshold for a RNAV approach. The MSA is not an operational altitude and may only be used in the event of an emergency.
US ATC requirements for clearing an aircraft for the approach and using direct to a step down fix between the IF and the FAF include:
If the fix is an IF, then the intercept angle may be up to 90 degrees.
Activating the approach can be dangerous if you passed the IAF already. In that case, the AP (assuming you are flying on the AP) will turn the aircraft around to the IAF. Better is indeed to start loading the approach AFTER you listened to the ATIS and/or know which runway to expect and not to do this already early on in the flight. This way, the whole flight you will have correct fuel estimates and when approaching the field and having copied the ATIS, you can load the approach without having to worry about if you will have enough fuel or not (in general, that it).
There used to be a problem with activating vectors to final as well as it would delete most of the intermediate fixes in the flightplan and thus you would not be able to easily refer/relate to them when ATC would address them or send you off to one of them. Now, this problem is mostly solved in later releases. The solution was to activate a leg of the approach instead. I never did/do that but will activate vectors to final as soon as I know I will be getting vectors and am flying on an assigned heading.
Sometimes I will be asked if I want to fly the approach on the other runway instead (while already on vectors to the other approach). This happens if there is not much wind and I could fly direct to the FAF on long final of a GPS approach and am already flying in that direction. It is all very easy to just load another procedure. It will automatically drop the earlier loaded one.
Flying back to my homebase Rotterdam I often am asked if I am interested in flying a shortened ILS approach. I sometimes do accept this, which saves me flying outbound on the downwind leg for longer than strictly necessary.
I have to say… despite having been in “computers” since the 1970s, I still fly all navaid based approaches using the HDG mode (till the intercept, either onto the LOC, or onto the GPS OBS track which represents the inbound VOR/NDB radial) and I fly all GPS approaches by selecting the approach, saying Yes to “insert into flight plan” question (KLN94), and flying in HDG or NAV mode until the enroute phase’s waypoints are exhausted and then setting a DTC to the cleared IAF.
It is dead easy to fly the outbound leg of UK/European procedural approaches in HDG mode. Just estimate the wind offset, fly straight to the fix, and then fly the heading, twiddling it to achieve the correct GPS track, then turn onto the inbound leg and intercept as described above.
The problem with using the GPS in NAV mode to fly navaid based approaches (except, presumably, the ILS which is flown with, hmmm, the ILS receiver) is that if it does something you didn’t expect, you aren’t going to find out until it has turned the aircraft in some weird direction and then you end up going all over the place sorting it out. To sort it out, you need superb situational awareness, which everybody with a moving map GPS has anyway, but if you have that SA, why not just keep things simple and fly the approach as it is drafted, in HDG mode?
That way, you don’t get the “WTF is it doing now” moments (as in the Airbus jokes).
In all cases I know of in Europe, one gets one of these, when approaching the end of the enroute phase (all assume autopilot or flight director use):
The above is for my 1990s avionics, with which I can trivially and accurately fly any procedure printed on any approach plate I have ever seen (legally or otherwise). Is it really not possible to go back to basics and exert that level of control over what happens with a GTN box?
Obviously, there are some notable differences between what is possible to control at lower levels in the U.S. (where most of the “lower” States have radar coverage even at very low levels (see Atlas of Radar Coverage of Lower 48 CONUS Border States At 500’ and 1000’)) and Australia.
Very good point. Different countries have different operational needs. Here in the US, although radar is widely available at low levels, it is not the controlling factor. Most of the US has class E airspace with a floor at either 1200 AGL or 700 AGL around airports where approaches are available, with class G airspace under the class E floor. A good deal of this airspace does not enjoy radar coverage at low levels, but requires an IFR clearance to operate under IFR in this airspace. Most approaches at non towered airports commence in class E airspace and terminate in class G airspace. No approaches commence in class G airspace. The reverse is also true at airports that are located in class G airspace as an IFR flight commences in class G, but an ATC clearance is required prior to entering class E airspace when conditions are IMC. If conditions in class G are IMC, a clearance isn’t technically required, but without a prior ATC clearance that only applies upon entering class E airspace, the FAA has deemed this process to violate 91.13 (careless and reckless operation). The point is that although IFR operation in IMC in US class G airspace is permitted, one needs a prior clearance to operate in class E airspace under these conditions.
A pilot had his licence suspended because of departing in IMC conditions in class G where there was a low and thin overcast. He claimed he did not need a clearance in class G according to the regulations and was on top in VMC conditions prior to entering class E airspace and did not require an IFR clearance. He was found to be in violation of 91.13 because without a clearance to enter class E airspace under IFR, another IFR aircraft could have been making an approach to the airport. Under ATC rules at such an airport, only one aircraft operating under IFR is permitted in the airspace at a time, so had the pilot waited until he was provided an IFR departure clearance, separation from other IFR traffic would have been assured. Of course separation from VFR traffic under the overcast is see and avoid, so multiple VFR aircraft may be in the airspace at the same time.
The pilot in question could also have been charged with violation of 91.155 (basic VFR minimums) as his statement effectively admitted he violated this regulation. 91.155 only requires 1 SM and clear of clouds in class G airspace, but in class E airspace the visibility and cloud requirements are increased to 3 SM, 500 feet below, 1,000 feet above, and 2,000 feet lateral separation from clouds. Once on top of the overcast and in VMC, as soon as he reached the class E boundary at 701 AGL, he could not be 1000 feet above the cloud deck.
I have to say… despite having been in “computers” since the 1970s, I still fly all navaid based approaches using the HDG mode
Peter, you are using what I would call manual roll steering! 
I call it “making the thing do what you want it to do, with no ambiguity”
I didn’t even mention European GPS databases often containing incomplete procedures… they are complete allright for GPS approaches but VOR or NDB procedures often have pieces missing.
