How to use RNAV substitution on the IR skills test
By Rory Bennett (ATPL, FI: CPL, IR, ME, UPRT) · Published 4 June 2026 · Updated 5 June 2026
Direct answer
On a UK IR skills test, RNAV substitution lets you use the FMS/RNAV system in place of conventional VOR, NDB and DME guidance. Standards Document 1 permits it in every phase of flight except lateral guidance on the final approach segment of an instrument approach. Departure, en route and arrival may be flown without limitation; the hold and the approach carry specific test limitations[1].
What is RNAV substitution?
CAP 1926 defines RNAV substitution as the ability to use the FMS/RNAV system instead of conventional radio navigation aids[2]. It lets you fly a procedure that was designed around a VOR, NDB or DME using your area navigation system for primary guidance, without monitoring the raw data of those ground-based aids.
It works in one of two ways. A fix substitution uses the area navigation system to substitute a position defined by a ground-based aid. An FMS Coded Overlay is a database coding of a complete conventional procedure that, once selected, has the appearance of an RNAV procedure[2].
Can you use RNAV substitution on the IR skills test?
Yes. Standards Document 1 states that RNAV substitution may be used in all phases of flight in UK airspace, except to provide lateral guidance in the final approach segment of an instrument approach procedure[1]. Its most common use on test is to make a profile flyable when the aircraft is not fully equipped: where the avionics do not include an ADF and/or DME, the examiner is advised to establish at an early stage whether that lack imposes limitations on the available procedures and destinations, or whether substitution will allow the planned profile to be flown[1].
Substitution does not remove the conventional skills the examiner needs to see. The route and profile are selected so the examiner can assess a mixture of PBN, VOR and ADF tracking, using both beam bar (HSI/CDI) and single-needle (RMI/RBI) displays[1]. During the test the examiner will deny or limit some systems and displays in order to assess that wider range of skills.
What equipment and approval do you need?
CAP 1926 sets the operational criteria. The FMS/RNAV installation must be certified for RNAV 1, RNP 1 or Advanced RNP, and use of substitution is restricted to operators and pilots authorised for one of those specifications[2]. The operator or pilot must document a policy for its use, standard operating procedures, contingency procedures for loss of GNSS, and training.
Two equipment points bite directly on test day. The navigation database must be current[1][2], and any navaid or procedure you intend to substitute must actually be coded in the database so it can be used as a waypoint or selected and flown[2].
Can you use RNAV substitution in the departure, en route and arrival?
These phases are the straightforward part. The operating procedures in CAP 1926 may be used in the departure, en route and arrival sections of the test without limitation[1]. Within scope, that lets you use the area navigation system to navigate to and from a VOR or NDB, hold over a VOR, NDB or DME fix, fly a DME arc, and fly an overlay of a conventional departure, arrival or route[2].
How do you fly the hold with RNAV substitution?
The hold is where the test tightens up. Standards Document 1 requires the following[1]:
- Fly a normal timed hold by manual heading (or as required on the approach plate), having temporarily halted automatic waypoint sequencing when approaching the holding fix.
- RNAV guidance may be used to achieve and maintain the inbound holding course, but FMS steering, such as selecting "Hold at Waypoint" to fly the racetrack, is not acceptable.
- Where the aircraft is so equipped, entry to and maintenance of the hold should be flown on single-needle information rather than a CDI display.
- GNSS map information is denied during hold entry and maintenance, so the examiner can assess your situational awareness.
On a Garmin G1000, the function that meets the "halt automatic waypoint sequencing" requirement is the OBS softkey. Enabling OBS Mode suspends the automatic sequencing of waypoints in the GPS flight plan and retains the current active-to waypoint, here the holding fix, as the navigation reference even after you pass it, so the box will not sequence on to the next leg as you fly the racetrack[3]. A course line is drawn through that waypoint, and you set the inbound holding course on it with the CRS knob[3]. That is exactly the permitted use, RNAV guidance to capture and maintain the inbound course, while you fly the entry and the timed pattern by hand on heading and the clock[1]. Because OBS only holds the active-to fix and a selected course, it is not the FMS racetrack steering ("Hold at Waypoint") that the test prohibits.
You can practise OBS mode in the pro simulator: in the JustFly sandbox, switch the GPS to OBS mode, set your inbound holding course on the selector, and fly the racetrack by hand against it.
Can you use RNAV substitution on the approach?
Any approach you fly must be coded in the GNSS database, and examiners and applicants should check that the planned approach is included before the flight[1]. With that done, the approach limits are[1]:
- The initial approach segment of a non-RNP procedural approach may be flown using RNAV substitution, but a conventional lateral navigation mode must be selected and used once the base turn has been entered.
- Substitution may not provide lateral guidance in the final approach segment; that segment is flown on conventional lateral guidance.
- Substitution may be used again from the missed approach point onwards.
This matches CAP 1926, which permits flying an overlay of a conventional approach except as lateral guidance in the final approach segment, and requires the whole procedure, including the initial, intermediate and missed approach segments, to be coded as an overlay before it can be selected and executed[2].
Does RNAV substitution replace the mandatory RNP approach?
What must you still be able to fly without substitution?
Substitution is a tool for making a profile flyable, not a way around conventional competence. The CAA considers it important for all applicants to be trained to competence in the full range of IFR procedures they are likely to meet once rated, including departures, arrivals, approaches, missed approaches and holds predicated on ADF. The ATO must still include training in the operation and use of ADF and NDB, and applicants must be competent to fly any published instrument procedure[1].
That is also why the skill test oral can ask you to discuss to what extent GNSS can be substituted for conventional VOR, ADF and DME navigation aids[1]. Knowing the rule, all phases except final approach lateral guidance, plus the hold and approach limits above, is the answer the examiner is looking for.
Try RNAV substitution in the simulator
The best way to get a feel for substituting GNSS for conventional aids, and for the hand-flown discipline the test demands, is to fly it. Open the free-form JustFly tool in the pro simulator and work through these, each mapped to a CAP 1926 application:
- Navigate to and from a VOR on GNSS. Tune and identify a VOR, then track to the station and back out on a chosen radial using the GPS/GNSS guidance for primary navigation while keeping the raw data in your scan as a cross-check. This is the "navigation to or from a VOR" application of substitution.
- Hold the test way. In the Holding Trainer, fly the entry and the pattern on single-needle (RMI/RBI) with manual heading and timing, without leaning on the moving map, exactly as Standards Document 1 requires in the hold.
For the broader regulatory picture this sits inside, see UK CAA IFR flight planning, and to drill the conventional tracking and single-needle holding the examiner still wants to see, work through how to determine hold entry.
Common mistakes
- Letting the FMS fly the hold with "Hold at Waypoint" or automatic sequencing. Standards Document 1 paragraph 3.9.4 requires a normal timed hold flown by manual heading with automatic waypoint sequencing halted approaching the fix. RNAV guidance may be used to achieve and maintain the inbound course, but FMS steering of the racetrack is not acceptable on test.
- Leaving the GNSS moving map displayed during the hold. The map is denied during hold entry and maintenance so the examiner can assess your situational awareness. Fly the entry and the pattern on single-needle (RMI/RBI) information where the aircraft is so equipped.
- Flying the final approach segment laterally on the GPS overlay. Substitution may not provide lateral guidance in the final approach segment of an instrument approach. Select a conventional lateral navigation mode once the base turn is entered and fly the final approach segment on conventional guidance.
- Assuming a substituted conventional approach counts as your RNP approach. It does not. An approach based on conventional aids flown using RNAV substitution does not satisfy the requirement that one approach during the IR skill test must be an RNP approach. Plan a separate, genuine RNP approach.
- Turning up without an ADF and assuming substitution removes the need to be ADF-competent. Substitution may let the planned profile be flown, but the ATO must still train ADF and NDB to competence and you must be able to fly any published instrument procedure (Standards Document 1 paragraph 2.2.4). Flying with a stale database is a separate, common failure, the database must be current.
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Frequently asked questions
What is RNAV substitution?
RNAV substitution is the ability to use the FMS/RNAV system instead of conventional radio navigation aids, as defined in CAP 1926. It relies on either a fix or an FMS Coded Overlay, a database coding of a conventionally-defined procedure, so the aircraft can fly a VOR, NDB or DME procedure using GNSS-based guidance.
Can I sit my IR skills test in an aircraft with no ADF or DME?
It may be possible. Standards Document 1 paragraph 2.2.3 says where the aircraft lacks ADF and/or DME the examiner establishes at an early stage whether the limitation affects the available procedures, or whether RNAV substitution will allow the planned profile to be flown. The ATO must still have trained you in ADF and NDB to competence.
In which phases of flight can RNAV substitution be used on the test?
Standards Document 1 paragraph 3.9.1 allows RNAV substitution in all phases of flight in UK airspace except to provide lateral guidance in the final approach segment of an instrument approach. Departure, en route and arrival may use it without limitation; the hold and the approach carry specific test limitations.
Can I fly the final approach segment on GPS using substitution?
No. Substitution may not provide lateral guidance in the final approach segment of an instrument approach procedure. On a non-RNP procedural approach you select a conventional lateral navigation mode once the base turn is entered and fly the final approach segment using conventional guidance.
Can I use the FMS to fly the holding pattern?
Not as automatic steering. The hold must be flown as a normal timed hold by manual heading, with automatic waypoint sequencing halted approaching the fix. RNAV guidance may be used to achieve and maintain the inbound holding course, but FMS steering such as selecting "Hold at Waypoint" is not acceptable, and the GNSS map is denied during the hold.
Does an RNAV-substituted approach count as the mandatory RNP approach?
No. The use of RNAV substitution during an approach based on conventional aids does not satisfy the requirement that one approach during the IR skill test must be an RNP approach. You must fly a separate, genuine RNP approach.
What equipment and approval do I need to use RNAV substitution?
CAP 1926 Chapter 5 requires the FMS/RNAV installation to be certified for RNAV 1, RNP 1 or Advanced RNP, and the operator or pilot to be authorised for one of those specifications, with a documented policy, standard operating procedures and training. The navigation database must be current and the procedures retrieved from it.
Sources
- UK Civil Aviation Authority, Standards Document 1, Version 12: Notes for the Guidance of Examiners and Applicants taking the Initial Instrument Rating and En Route Instrument Rating Skill Test (Aeroplanes), December 2025. Sections 2.2.3 to 2.2.4, 3.6.12 to 3.6.13, and 3.9. caa.co.uk/publication/download/12805
- UK Civil Aviation Authority, CAP 1926: UK Guidance for Operators/Pilots, RNAV Substitution, 2nd edition, April 2025. Chapters 2 (Definitions), 4 (Scope and Limitations), 5 (Operational Criteria) and 6 (Operating Procedures). caa.co.uk/CAP1926
- Garmin Ltd., G1000 Integrated Avionics System Pilot's Guide for the Diamond DA42, document 190-00649-03 Rev. B, section "OBS Mode" (Flight Instruments). Used only for the G1000 procedure in the hold section; it carries no regulatory claim.
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This article does not constitute flight instruction. Always defer to the guidance of your qualified flight instructor and to current charts and procedures or regulations published by your country's aviation authority.
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