ADS-B and Call Sign Confusion

The ADS-B mandate has arrived, and with it comes the potential for another source of confusion. Most pilots flying with ADS-B systems have a display of traffic in the cockpit, either on a moving map that’s part of a GNSS navigation system or on a tablet like an iPad running an app such as ForeFlight, Garmin Pilot, or FlyQ. These traffic systems usually show the identification of other aircraft, either the registration number or the airline flight number.

ADS-B traffic (TIS-B) as shown in ForeFlight

When ATC issues traffic advisories–for example, “Cessna 1234A, traffic 2 o’clock, 4 miles, a Southwest 737”–it might be tempting to include the target identification in your acknowledgement. For example, “Cessna 1234A, we have Southwest 2345 in sight,” or “Southwest 2345 in sight, Cessna 1234A.”

If that sounds odd, watch some aviation videos on YouTube. At least one pilot flying an airplane with a new glass panel has made a habit of such replies.

For obvious reasons, it’s a bad idea to include another aircraft’s identification or call sign when you respond to ATC. In fact, the FAA’s December 2019 update to AC 90-114 Automatic Dependent Surveillance-Broadcast Operations anticipates this issue:

2.4.3.4 Unless initiated by the controller, pilots should typically not use the call sign or Aircraft Identification (ACID) of observed traffic in radio communications, as this could create confusion for both ATC and pilots monitoring the frequency.

AC 90-114B

So even if you’re equipped with the latest technology, stick to the standard replies when ATC points out traffic:

“Cessna 1234A, traffic 2 o’clock, 4 miles, a Southwest 737.”

“Cessna 1234A, we have the Southwest 737 in sight,” or “Traffic in sight, Cessna 1234A.”

Transiting Airspace with Flight Following

Pilots who are receiving radar advisories, better known as VFR Flight Following, often wonder if they will be cleared to enter airspace along their route.

For example, assume you’re flying VFR between Albany, OR (S12) and Scappoose, OR (KSCP).

(To see the route below on charts at SkyVector.com, click here.)

As you can see on the chart below, the direct route takes you over Salem (KSLE), a Class D airport; just west of the Class D airspace at Aurora, OR (KUAO); and later through the Class D airspace at Hillsboro (KHIO). The course also tracks just west of the busy Class C airspace that surrounds Portland International Airport (KPDX).

After takeoff, you contact Cascade Approach for flight following, get a squawk code, and, without restrictions from ATC, proceed on the direct route to KSCP. An overcast layer at 3000 ft. MSL restricts your cruise to at or below 2500 ft.

Do you have to contact the towers at KSLE and KHIO for permission to transit their airspace? Although you’ll remain legally clear of the Class D airspace at KUAO if you can remain on the direct course, what if you need to zig and zag to avoid clouds? Should you contact Aurora Tower? What about the Class C airspace at KPDX?

The September 2017 issue of Air Traffic Procedures Bulletin (PDF), a newsletter for air traffic controllers published by the FAA, clarifies the roles of pilots and air traffic controllers when pilots are receiving flight following. The bulletin notes that pilots and controllers have shared responsibility.

VFR Aircraft Receiving Radar Advisories (VFR Flight Following) Approaching Class D

What are ATCs responsibilities? Who is responsible for the pilot’s communication responsibility within the Class D surface area?

Many times, pilots receiving VFR Radar Advisories believe that as long as they are talking to one ATC facility, they have fulfilled their responsibility for entering a Class D airspace. Pilots may believe that controllers will tell them when/if they are approaching a Class D surface area. As controllers, we have a responsibility to coordinate with the appropriate ATC facility having jurisdiction over the airspace.

First, controllers must follow the guidance in Air Traffic Control (JO 7110.65, PDF available here):

As controllers, we have a responsibility to coordinate with the appropriate ATC facility having jurisdiction over the airspace, FAA Order JO 7110.65W states:

2-1-16. SURFACE AREAS

b. Coordinate with the appropriate control tower for transit authorization when you are providing radar traffic advisory service to an aircraft that will enter another facility’s airspace.

NOTE− The pilot is not expected to obtain his/her own authorization through each area when in contact with a radar facility.

But the bulletin notes that pilots also have a regulatory requirement to establish two-way communications before entering Class D or Class C airspace, as noted in the AIM and other sources.

The pilot’s responsibility to meet their radio communication requirement to enter Class D airspace is NOT eliminated when receiving VFR Radar Advisories. The Aeronautical Information Manual, 3-2-1, states:

d. VFR Requirements. It is the responsibility of the pilot to ensure that ATC clearance or radio communication requirements are met prior to entry into Class B, Class C, or Class D airspace. The pilot retains this responsibility when receiving ATC radar advisories. (See 14 CFR Part 91.)

To resolve this conflict, the bulletin goes on to explain:

Since both the controller providing VFR Radar Advisories and the pilot who is receiving the advisories have a clear responsibility, there can be some confusion about which party is communicating with the ATC facility having jurisdiction over the Class D surface area. 14 CFR 91.129 includes language that specifies that it is the pilot’s overall responsibility for complying with the Class D communications requirement.

There are a few ways controllers can assist pilots when providing VFR Radar Advisories that will ultimately help with controller workload. Since the pilot is responsible for their Class D communication requirement, if the controller coordinates with the ATC facility having jurisdiction over the surface area, let the pilot know, so they do not query you. If you are too busy to coordinate, you are required to terminate VFR Radar Advisories in a timely manner so the pilot is able to contact the Class D ATC facility prior to entry.

It’s also important to note that air traffic control facilities have letters of agreement (LOA) to establish local procedures, such as entry and exit routes at busy airports, handoffs between facilities, and similar matters. These LOA are not typically published for pilots. An LOA may allow an approach facility to send aircraft under its control through a Class D surface area at specific altitudes and along certain routes. Or the LOA may streamline the coordination required before one controller allows an aircraft to enter another controller’s airspace.

For more information about your obligation to follow ATC instructions, see Compliance with ATC Clearances and Instructions—Even When VFR.

For more information on this topic, see BruceAir’s Guide to ATC Services for VFR Pilots.

Compliance with ATC Clearances and Instructions—Even When VFR

You are flying along a sunny day outside of Class B, C, or D airspace. Like many pilots, you’re taking advantage of VFR radar advisory services, commonly known as “flight following.”

(For details about these services, see AIM 4-1-15. Radar Traffic Information Service and BruceAir’s Guide to ATC Services for VFR Pilots.)

Out of the blue, the controller directs you to fly a new heading that will take you out of your way. Perhaps you’re instructed to stop a climb or descent, frustrating your attempts to fly most efficiently.

Must you comply with such instructions? Remember, you’re operating under VFR in Class E airspace, well away from strictly controlled areas such as Class B and Class C airspace. (For a good review of airspace, start with Airspace for Everyone [PDF] from AOPA Air Safety Institute.)

The short answer is “yes.” See 14 CFR §91.123 Compliance with ATC clearances and instructions, which states in part:

…(b) Except in an emergency, no person may operate an aircraft contrary to an ATC instruction in an area in which air traffic control is exercised.

Many pilots argue about the applicability of that rule in the situation described here, and they quibble about distinctions between clearances and instructions.

But the FAA has made its position clear. See, for example, the Karas letter from 2013, issued by the office of chief counsel. That letter notes in part:

Section 91.123 deals with compliance with ATC clearances and instructions. Section 91.123(b) states: “Except in an emergency, no person may operate an aircraft contrary to an ATC instruction in an area in which air traffic control is exercised.”

Pilots flying in controlled airspace must comply with all ATC instructions, regardless of whether the pilot is flying VFR or IFR, in accordance with § 91.123(b). ATC instructions include headings, turns, altitude instructions and general directions. The Pilot/Controller Glossary of the Aeronautical Information Manual (AIM) defines ATC instructions as “[d]irectives issued by air traffic control for the purpose of requiring a pilot to take specific actions; e.g., ‘Tum left heading two five zero,’ ‘Go around,’ ‘Clear the runway. ‘” See AIM, Pilot/Controller Glossary. In contrast, the Glossary defines advisory as “[a]dvice and information provided to assist pilots in the safe conduct of flight and aircraft movement.” Id.

A pilot flying VFR in Class E airspace, which is controlled airspace, is not required to communicate with ATC; however, if a pilot is communicating with ATC and ATC issues an instruction, the pilot must comply with that instruction.

The last sentence is key, and straightforward:

…if a pilot is communicating with ATC and ATC issues an instruction, the pilot must comply with that instruction.

That statement is also general, in that it applies even if you’re talking to a control tower, not a radar facility.

Of course, as pilot in command, you have the authority—and the responsibility—to refuse instructions that would, for example, send you into the clouds while operating under VFR. Such situations require you to tell ATC that you’re unable to comply with instructions and to request an alternative directive. See, for example, this statement from AIM 4-1-18:

e. PILOT RESPONSIBILITY. THESE SERVICES ARE NOT TO BE INTERPRETED AS RELIEVING PILOTS OF THEIR RESPONSIBILITIES TO SEE AND AVOID OTHER TRAFFIC OPERATING IN BASIC VFR WEATHER CONDITIONS, TO ADJUST THEIR OPERATIONS AND FLIGHT PATH AS NECESSARY TO PRECLUDE SERIOUS WAKE ENCOUNTERS, TO MAINTAIN APPROPRIATE TERRAIN AND OBSTRUCTION CLEARANCE, OR TO REMAIN IN WEATHER CONDITIONS EQUAL TO OR BETTER THAN THE MINIMUMS REQUIRED BY 14 CFR SECTION 91.155. WHENEVER COMPLIANCE WITH AN ASSIGNED ROUTE, HEADING AND/OR ALTITUDE IS LIKELY TO COMPROMISE PILOT RESPONSIBILITY RESPECTING TERRAIN AND OBSTRUCTION CLEARANCE, VORTEX EXPOSURE, AND WEATHER MINIMUMS, APPROACH CONTROL SHOULD BE SO ADVISED AND A REVISED CLEARANCE OR INSTRUCTION OBTAINED.