≡ Menu

Can I Use My GPS When An Arrival Requires DME?

Question from a reader:

While Reviewing the CLAMP SIX arrival into Sarasota, FL I see the note “DME Required”. Can I fly this arrival if I don’t have DME but have an IFR certified GPS?

Many pilots are now using an IFR certified GPS while flying enroute. We know our GPS can substitute for DME enroute but occasionally I will get questions concerning STARs (Standard Terminal Arrival Procedures).

The reason this question occasionally arises is due to a note on certain arrival charts stating DME is required. The same notation does not appear on the enroute charts and is not seen in many of our normal IFR flying. Of course substituting our GPS is subject to certain restrictions listed below.

Restrictions when Substituting GPS for ADF or DME

The equipment must be installed in accordance with appropriate airworthiness installation requirements and operated within the provisions of the applicable POH/AFM, or supplement.

The required integrity for these operations must be provided by at least en route RAIM, or equivalent.

WPs, fixes, intersections, and facility locations to be used for these operations must be retrieved from the GPS airborne database. The database must be current. If the required positions cannot be retrieved from the airborne database, the substitution of GPS for ADF and/or DME is not authorized

Procedures must be established for use when RAIM outages are predicted or occur. This may require the flight to rely on other approved equipment or require the aircraft to be equipped with operational NDB and/or DME receivers. Otherwise, the flight must be rerouted, delayed, canceled, or conducted under VFR.

The CDI must be set to terminal sensitivity (1 NM) when tracking GPS course guidance in the terminal area.

A non-GPS approach procedure must exist at the alternate airport when one is required. If the non-GPS approaches on which the pilot must rely require DME or ADF, the aircraft must be equipped with DME or ADF avionics as appropriate.

Charted requirements for ADF and/or DME can be met using the GPS system, except for use as the principal instrument approach navigation source.

Example 1:

Let’s review the CLAMP SIX Arrival to Sarasota-Bradenton airport in Florida. (KSRQ) In the bottom left corner of the plan view you will see “DME Required”. DME is required to identify BOATS and WALTR intersections.

If you are someone who normally flies RNAV arrivals this might make you pause and think for a moment because you don’t normally see this note. We can fly this arrival if we don’t have DME, have an IFR certified GPS, and comply with the restrictions above.

Example 2:

Review the DYLIN FOUR arrival for Newark Liberty Airport in New Jersey to determine if DME is required. On the chart there is no note stating DME is required but for the portions of the arrival above FL240 we need to remember we must have DME per 91.205.

If we have an IFR Certified GPS then we can fly this without DME because we can substitute GPS for the DME. If we don’t have a GPS we will be required to use DME for the portions of the arrival above FL240. If we are flying this arrival below FL240 we will not need GPS or DME.

Conclusion:

If you have been flying with an IFR certified GPS, especially a WAAS certified GPS, you may believe you will no longer be concerned with regulations regarding DME. This is not true since you will still need to understand the rules concerning the substitution of DME. I hope next time you are flying an arrival with the note “DME Required” you will be confident in knowing if you are required to have DME.

Recommended Reading:

Alternate Filing With A WAAS Certified GPS


{ 2 comments… add one }
  • Mike Hunter May 18, 2013, 1:00 pm

    Very nice explanation. Now. Why does the KSRQ ILS or LOC RWY 32 (Amdt 8 13jan11) say “DME OR RADAR REQUIRED” and KSRQ VOR RWY 32 (Amdt 10 13jan11) not require DME?

    Yes, I’ve read AC90-108 dated 3/3/11. And thought I understood it to say exactly what you’ve outlined. GPS meeting the AC may be substituted for DME. So…why would one chart say DME is required, but the other not? Thanks!

  • CarlValeri May 21, 2013, 11:08 am

    Great question which deserves an explanation in a future blog post. The short answer to your question is without DME and radar you would not be able to navigate to fly the ILS or LOC to 32.

    Look for an upcoming blog post for a more complete explanation.

    Thanks for the question,

    Carl.

Leave a Comment