Can you begin descending before becoming established on the STAR arrival route? Here's what you need to know...

Review: "Descending Via" The STAR

Before the scenario, let's review what you should know about Standard Terminal Arrival Procedures (STARs). Arrival procedures streamline inbound IFR traffic into defined routes. They usually start with a transition. On the TEJAS 4 Arrival below, there are several transitions, and one of them is the Corpus Christie VOR. On this particular arrival, all of the transition routes merge, and the aircraft join the same route at GMANN.

ATC organizes arriving traffic in three dimensions. They're managing altitude, lateral path, and airspeed to keep traffic separated. Arrivals help with all three.

A descend via is an abbreviated ATC clearance that requires compliance with a published procedure's lateral path and associated speed restrictions and provides a pilot-discretion descent to comply with published altitude restrictions until descending to the 'Bottom Altitude' published on the STAR.

But what happens when you're cleared direct to a fix on the STAR and told to 'descend via'?

Scenario: Direct To A STAR Fix

Approaching Chicago O'Hare from the Northwest at FL180 in a regional jet, you receive the following clearance:

View full MADII 4 STAR chart here.

On the STAR, you need to cross GURNN at or below FL180. You're already at FL180 roughly 20 miles from GURNN. The next fix, CHDRR, must be crossed at 14,000 feet MSL.

If you stay at your current altitude until you're established on the STAR, you'll have 10 miles to descend 4,000 feet from FL180 to 14,000 feet.

Chicago asks you to maintain best forward airspeed. So when can you start your descent?

Can You Descend Before Reaching GURNN?

The short answer: Yes, you can begin your descent right away to meet the crossing restrictions of the STAR.

In this case, you can begin your descent as soon as you receive the "descend via" clearance from ATC. Even though you're not established laterally on the arrival, ATC has assumed responsibility for obstacle separation as long as you remain above the MEAs. Without the ability to descend, meeting subsequent crossing restrictions might be impossible. Here's what a descend via clearance authorizes you to do (AIM 5-4-1a):

• Descend at pilot's discretion to meet published restrictions and laterally navigate on a STAR.
• When cleared to a waypoint depicted on a STAR, to descend from a previously assigned altitude at pilot's discretion to the altitude depicted at the waypoint.
• Once established on the depicted arrival, to descend and to meet all published or assigned altitude and/or speed restrictions.

If no altitude is depicted at the fix you've been cleared to along a STAR, ATC is required to assign you a crossing altitude. If you were cleared to FALLS (FAH) to "descend via" the MADII 4 arrival, the controller must issue you a crossing restriction at FAH (AIM 5-4-1a).

Have You Received A "Descent Via" Clearance Recently?

Have you ever gotten a confusing "descend via" clearance? Tell us in the comments below.