# Why does DME colocated with VOR require more separation?

In earlier versions of ICAO Doc 4444 (Amendment 9 and earlier), two aircraft were deemed to be laterally separated if they were departing a VOR on radials which diverged by at least 15 degrees and if at least one of the aircraft was at least 15 NM from the VOR.

However, as of Amendment 10, this distance requirement has increased to 17 NM (or more) if the distance measurement is based on DME:

When distance from VOR is based on co-located DME, distance of one aircraft should be at least 17 NM from VOR below FL190 and 18 NM from VOR at or above FL190.

What made ICAO change this separation?

• Welcome to Aviation.SE! Can you quote the relevant section from ICAO Doc 4444? Jun 8, 2022 at 6:09
• ICAO DOC 4444 AMDT 10 LATERAL SEPARATION AND MINIMA Jun 8, 2022 at 6:53
• The request is to quote it in your question rather than expect people to look it up.
– GdD
Jun 8, 2022 at 11:12
• Voting to close as "unclear" until the question is clarified enough that I can understand what's being asked without needing to google-search then read a lengthy document.
– Ralph J
Jun 8, 2022 at 14:18
• In ICAO Doc 4444, These is no mention of co-located DME. It is mentioned as an additional note in MATS Part I (India). However the reason may be the answer given by randomhead Jun 9, 2022 at 2:55

\begin{align} \mathrm{DME}^2 &= x^2 + h^2 \\ &= \left(15 \mathrm{~NM} \cdot \frac{6076 \mathrm{~ft}}{1 \mathrm{~NM}} \right)^2 + \left(19000 \mathrm{~ft} \right)^2 \\ \mathrm{DME} &= \sqrt{ 91140^2 \mathrm{~ft}^2 + 19000^2 \mathrm{~ft}^2 } \\ &= 93100 \mathrm{~ft} \\ &= 15.3 \mathrm{~NM} \end{align}