What is the lower limit of the jet route altitude stratum?

What is the lower limit of the jet route altitude stratum?

• A. FL140
• B. FL160
• C. FL170
• D. FL180

Answer: (D)

Jet routes are high-altitude airways used by turbojet and high-speed traffic, so they have a defined base altitude that marks the start of the jet-route system. The standard base for this jet-route stratum is Flight Level 180, which corresponds to 18,000 feet in standard atmosphere. This lower limit helps ensure adequate vertical separation from lower-altitude routes and weather, while matching performance and navigation considerations for jet aircraft. The other flight levels listed are all below this base and belong to lower or different enroute structures, not the jet-route system. Therefore, the lower limit of the jet route altitude stratum is Flight Level 180.

Jet routes are high-altitude airways used by turbojet and high-speed traffic, so they have a defined base altitude that marks the start of the jet-route system. The standard base for this jet-route stratum is Flight Level 180, which corresponds to 18,000 feet in standard atmosphere. This lower limit helps ensure adequate vertical separation from lower-altitude routes and weather, while matching performance and navigation considerations for jet aircraft. The other flight levels listed are all below this base and belong to lower or different enroute structures, not the jet-route system. Therefore, the lower limit of the jet route altitude stratum is Flight Level 180.