id: dme-arc title: DME Arc meta: Learn how to fly DME Arcs within Infinite Flight. order: 6 type: Advanced contributor: deercrusher #

DME Arc #

What is a DME Arc? #

Distance Measuring Equipment, abbreviated to DME; is most commonly used with a navigation aid (NAVAID) such as a VOR to provide distance to or from the beacon. A DME Arc is a curved route defined by a constant distance from one of these NAVAID’s with the arc distance essentially a radius of the circle around the NAVAID.

DME Arcs are most commonly found on the Initial approach segment, leading aircraft from the Initial Approach Fix (IAF) onto the Final Approach Course where the Intermediate and Final approach segments can be commenced.

Around the arc will be a series of published radials from the NAVAID that are used to indicate the start of the arc, when further descent can be made, and when a turn can be commenced to intercept the Final Approach Course.

Below is an example of what a DME Arc looks like on a chart; in this particular case, it leads aircraft onto the Final Approach Course for RWY04R in Honolulu (PHNL) via the ALANA IAF:

PHNL Chart

What is the Horizontal Situation Indicator (HSI)? #

The Horizontal Situation Indicator or HSI, is the primary instrument used for navigation in Infinite Flight. It consists of the following elements:

HSI Elements

DME Arc Flying Technique #

To enter an arc, aircraft are normally required to follow a radial which means that they are approaching the arc at a 90 degree angle. A 90 degree turn will require anticipation, we recommend using 1% of your groundspeed as an indicator of when to turn unless the chart specifies a distance.

Tip

: So if you are flying 180kts, you will need to start the turn at 1.8 miles to go!

Once established on the arc and to be able to follow the curved track keeping the DME distance the same, the aircraft heading would always need to be 90 degrees to the beacon (in nil wind conditions). However to fly this and match the radius of turn, the aircraft would need to adopt an angle of bank that varied continuously due to the effects of wind on the aircraft groundspeed. As this is impractical, the best technique is to break the arc up into a series of controlled heading changes instead, cutting slightly across the arc each time.

A predetermined heading change needs to be picked; 10 degrees is used in the example below but could be higher if you prefer! Once established on the arc (i.e. the correct distance from the beacon as published on the DME Arc, with a relative bearing of 90 degrees) a 10 degree turn can be made to ‘cut-across’ the arc. The bearing pointer will now read 5 degrees above the 90 degree line (actual relative bearing is 85 degrees) and the aircraft will begin to cut across the arc. As the aircraft approaches the arc again, the bearing pointer will begin to move until it has dropped 5 degrees below the 90 degree line (actual relative beading is now 95 degrees); at this point, another 10 degree cut-across can be made and the technique is repeated until the arc is complete.

DME Arc Flying Technique

In “HSI 1” above, you can see that the aircraft has made a 10 degree turn to begin cutting across the arc (the Bearing Pointer is now 5 degrees above the 90 degree relative bearing line). In “HSI 2”, the aircraft has now approached the end of the cut-across (the Bearing Pointer is now 5 degrees below the 90 degree relative bearing line). In “HSI 3”, the aircraft has now made another 10 degree turn to cut across the next segment of the arc (the Bearing Pointer is now 5 degrees above the 90 degree relative bearing line).

Tip

: When each cut-across is made, the DME will start off by indicating the published arc distance. This will then slightly decrease as the aircraft ‘cuts the corner’, however this should begin to return to the published arc distance before the next turn is made

If when approaching the 90 degree relative bearing line, the DME distance does not match the published arc distance, the following corrective action will need to be taken:

DME Distance Corrective Action
Lower than the published arc distance Maintain the heading for longer until the distance is reset before making your next cut-across turn
Higher than the published arc distance A larger cut-across turn will need to be made to re-establish on the arc

How to Set Up your Horizontal Situation Indicator (HSI) #

Step 1

: Tune the NAVAID by tapping the NAVAID from your Map or Mini Map, selecting the VOR/NDB from the list displayed, and then tap “Set NAV 1 (or 2)”

Step 2

: Display the VOR or NDB by tapping “NAV” on the Fly Screen to show the Avionics tab, and ensure that either BRG 1 (or 2) have NAV 1 (or 2) or ADF displayed (dependent on which NAVAID you tuned)

How to Fly a DME Arc #

Step 1

: Looking at the approach chart, establish which NAVAID is required, where the DME Arc starts/ends and what distance needs to be flown

Step 2

: Set up your Horizontal Situation Indicator (HSI) to help fly the DME Arc. If you are intercepting the Final Approach Course of a Precision/Non-Precision approach at the end of the DME Arc, make sure to have this tuned too if you can

Tip

: Although not required, it can be handy to put some of the waypoints or the approach itself into your Flight Plan to help you with position awareness

Step 3

: Plan what speed you are going to fly the procedure at. When inbound to the entry point of the arc, use your groundspeed to gauge when to turn onto your first heading (we recommend 1% of your groundspeed, so if you are at 180kts GS, start the turn at 1.8nm to the arc)

Tip

: We recommend not flying a DME Arc any faster than 180kts IAS to help reduce your workload; however, dependant on the aircraft type you may fly at a different speed. In any case, make sure to comply with all altitude/speed restrictions!

Step 4

: The initial heading on the arc should be one which puts the aircraft 90 degrees to the beacon, use the Bearing Pointer to help you

Step 5

: Adjust your heading by 10 degrees to ‘cut-across’ the arc, the Bearing Pointer should show a relative bearing of 85 degrees to the beacon

Step 6

: Monitor the Bearing Pointer and as it approaches a relative bearing of 95 degrees, turn another 10 degrees to ‘cut across’ the arc again

Step 7

: Make sure to continuously monitor the DME and ensure that this is roughly the same as the published DME distance, if it is different, correction action could be required

Step 8

: When you pass the final radial as indicated on the chart, continue the turn to intercept the Final Approach Course