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I saw this question in my Instrument Rating exam and I need to know which answer is correct, A or B.

Question: As far as the vertical reference of an aircraft during the final approach segment of an instrument approach procedure is concerned, a pilot:
A. may only use the local QNH setting on the altimeter sub-scale
B. may use the altimeter with QFE on the sub-scale

So far I have looked in ICAO 8168 and the SA CATS and CARS 2011 and this is what I found: 8168

8168

8168

This excerpt is from the SACAA CATS and CARS documents:

8 Approach and Landing
8.1 A QNH altimeter setting shall be made available to aircraft in approach clearances and in clearances to enter the traffic circuit.
8.2 A QFE altimeter setting, clearly identified as such, should be made available in approach and landing clearances on request.
8.3 The vertical positioning of aircraft during approach shall be controlled by reference to flight levels until reaching the transition level below which vertical positioning shall be reference to altitudes, except as provided for in paragraph 8.4.
Note: This does not preclude a pilot from using a QFE setting for terrain clearance purposes during the final approach to the runway.

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  • $\begingroup$ Please bear in mind that many of the SACAA exam questions are ambiguous or rather test your understanding of grammar and semantics. $\endgroup$
    – Raffles
    Sep 10 '20 at 20:11
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I have never been given a QFE to conduct an instrument approach in S.A. It does happen in some countries but then everyone has to use it. If you look on an approach chart you will see the vertical profile is given in terms of height above sea level so you wouldn't be able to conduct the approach with QFE set. Edit: The SACAA charts do show height of the waypoints of the vertical profile, but Jeppesen doesn't. The MDA and DH are given terms of elevation and height, but this is to use in conjunction with the radio altimeter. QFE might be used by aerobatic pilots or some military operations but I think its use is rare. Having said that, the AIP does appear to allow the use of QFE on a second altimeter during the final approach see note(2) and point (f) below. Therefore it appears that B is the answer the CAA is looking for. Using the word "only" in answer A would make it incorrect.

Please look at the AIP here with particular attention to the Altimeter Setting Procedures, I will try elaborate in due course.

Firstly the AIP says

The altimeter setting procedures in use conform to those contained in ICAO Doc 4444 ATM/501 Procedures for Air Navigation Services and ICAO Doc 8168 OPS/611 Procedures for Air Navigation Services - Aircraft Operations

Then it says

During flight in the vicinity of an aerodrome at or below a fixed altitude called the transition altitude, an aircraft shall be flown at altitudes determined from an altimeter set to sea level pressure (QNH) and its vertical position shall be expressed in terms of altitude.

Further down below it says

On reaching the transition level at least one altimeter within the aircraft shall be set to the QNH and thereafter the vertical positioning of such aircraft shall be by reference to altitudes.

Note 1: On reaching the transition level, pilots shall reset their altimeters to the QNH without requesting Air Traffic Control (ATC) permission to do so and without notifying Air Traffic Control (ATC) that the change has been made.

Note 2: This does not preclude a pilot from using a QFE setting for terrain clearance purposes during the final approach to the runway.

f) During the approach to land, terrain clearance may be determined by using either a QNH altimeter setting (giving altitude) or a QFE setting (giving height above the QFE datum)

I believe the intention is to allow the pilot the discretion of using a second altimeter with the QFE set, but when you talk to ATC it will be with reference to the altimeter having QNH set.

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  • $\begingroup$ Thank you Raffles for your detailed response. I also thought that QNH was the only vertical reference to be used on instrument approaches. However, in the process of researching this question, I recalled that radio altimeters use QFE on CAT II and III approaches. Since the question doesn't specify a specific instrument approach and is referring to any instrument approach, I thought that it might rule out "may use only QNH" as an answer and make answer B the more correct answer. What do you think? $\endgroup$ Sep 11 '20 at 7:46
  • $\begingroup$ Hi Student_Pilot, I'm beginning to think the same, due to the wording of the two answers. I put the question on Avcom and some guys also think the same. I looked in ICAO document 4444 and the wording is the same as the AIP (so the CAA copied 4444). I will modify my answer shortly. $\endgroup$
    – Raffles
    Sep 11 '20 at 10:21

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