Welcome Guest. Sign in or Signup

2 Answers

DME Requirement

Asked by: 18198 views General Aviation

Why is DME required 24000 msl and above? Why 24000 MSL instead of 23000 MSL, 25000 MSL, etc……?

Ace Any FAA Written Test!
Actual FAA Questions / Free Lifetime Updates
The best explanations in the business
Fast, efficient study.
Pass Your Checkride With Confidence!
FAA Practical Test prep that reflects actual checkrides.
Any checkride: Airplane, Helicopter, Glider, etc.
Written and maintained by actual pilot examiners and master CFIs.
The World's Most Trusted eLogbook
Be Organized, Current, Professional, and Safe.
Highly customizable - for student pilots through pros.
Free Transition Service for users of other eLogs.
Our sincere thanks to pilots such as yourself who support AskACFI while helping themselves by using the awesome PC, Mac, iPhone/iPad, and Android aviation apps of our sponsors.

2 Answers



  1. John D. Collins on Apr 04, 2013

    Positive Control Airspace used to be at FL240 and above. It has since been lowered to FL180 and is now called Class A airspace. The original DME requirement was for FL240 and wasn’t moved to FL180 when the airspace definition changed. I don’t know the precise reason for the requirement, but since most turbo jet fly at or above FL240 and are high performance (high speed), it is more convenient to use distance for intersections than cross radials along the jetways. Also when radar is unavailable due to coverage or outage, having distance available for position reporting allows for simplified along track spacing. It is interesting to note that DME is only required above FL240 if VOR must be used to fly the route. If the aircraft is equipped with a suitable RNAV system, it may use the RNAV in lieu of the DME. Although Turbojet aircraft fly below FL240, they are mostly doing this during the departure and arrival phases of flight and don’t typically cruise below this altitude where slower turboprop and turbocharged aircraft often cruise in the range of the high teens to FL250. Regardless, the requirement for a DME or RNAV is met by the vast majority of all aircraft that fly IFR.

    From 91.205:

    (e) Flight at and above 24,000 feet MSL (FL 240). If VOR navigation equipment is required under paragraph (d)(2) of this section, no person may operate a U.S.-registered civil aircraft within the 50 states and the District of Columbia at or above FL 240 unless that aircraft is equipped with approved DME or a suitable RNAV system.

    +15 Votes Thumb up 15 Votes Thumb down 0 Votes



  2. Dan Chitty on Apr 04, 2013

    John,

    Thank you for the excellent explanation. I greatly appreciate the feedback.

    Regards,

    Dan

    +1 Votes Thumb up 1 Votes Thumb down 0 Votes


The following terms have been auto-detected the question above and any answers or discussion provided. Click on a term to see its definition from the Dauntless Aviation JargonBuster Glossary.

Answer Question

Our sincere thanks to all who contribute constructively to this forum in answering flight training questions. If you are a flight instructor or represent a flight school / FBO offering flight instruction, you are welcome to include links to your site and related contact information as it pertains to offering local flight instruction in a specific geographic area. Additionally, direct links to FAA and related official government sources of information are welcome. However we thank you for your understanding that links to other sites or text that may be construed as explicit or implicit advertising of other business, sites, or goods/services are not permitted even if such links nominally are relevant to the question asked.