What obstacle clearance and navigation signal coverage is a pilot assured with the minimum sector altitudes depicted on IAP charts?

MSA

Figure 1: IPH definition of MSA

Minimum Safe Altitudes are published for emergency use on IAP charts. MSAs provide 1,000 feet of clearance over all obstacles but do not necessarily assure acceptable navigation signal coverage. The MSA depiction on the plan view of an approach chart contains the identifier of the center point of the MSA, the applicable radius of the MSA, a depiction of the sector(s), and the minimum altitudes above mean sea level which provide obstacle clearance…. For RNAV approaches, the MSA is based on an RNAV waypoint. MSAs normally have a 25 NM radius….

Figure 2: An MSA And A Feeder Fix

Figure 3: IPH definition of feeder route

RESEARCH

The question is whether “cleared for the approach” constitutes permission to descend to the minimum safe altitude (MSA) associated with that approach. My first source was the FAA’s Instrument Procedures Handbook (FAA-H-8083-16A). Chapter 4, Approaches, and the excerpt shown in Figure 1. The IPH’s description of the MSA outlines more about how they are defined and appear on charts—refer to the planview for the RNAV (GPS) Runway 1 procedure on the opposite page for an example—but in no way qualifies the declarative statement that MSAs are solely for emergency use.

Meanwhile, the IPH section titled Instrument Approach Procedure Segments describes the means of descending from the en route environment to the initial, intermediate and final approach fixes. The MSA is not even mentioned. It does say, however, that “feeder routes provide a transition from the en route structure to the IAF. FAA Order 8260.3 (TERPS) criteria provides obstacle clearance for each segment of an approach procedure….” An example of a charted feeder route is reproduced in Figure 2 while Figure 3 is the IPH’s feeder-route description. And then we have terminal arrival areas, or TAAs.

For RNAV-equipped aircraft, according to the IPH, a TAA “provides a transition from the en route structure to the terminal environment with little required pilot/air traffic control interface for aircraft equipped with Area Navigation (RNAV) systems. TAAs provide minimum altitudes with standard obstacle clearance when operating within the TAA boundaries.” This section does mention the MSA, thusly: “Altitudes published within the TAA replace the MSA altitude. However, unlike MSA altitudes the TAA altitudes are operationally usable altitudes” (emphasis supplied).

Here’s where I think I’m starting to learn something. Continuing its discussion of TAAs, the IPH states (emphasis supplied), “An ATC clearance direct to an IAF or to the IF/IAF without an approach clearance does not authorize a pilot to descend to a lower TAA altitude. If a pilot desires a lower altitude without an approach clearance, request the lower TAA altitude from ATC. Pilots not sure of the clearance should confirm their clearance with ATC or request a specific clearance. Pilots entering the TAA with two−way radio communications failure…must maintain the highest altitude prescribed [in FAR 91.185(c)(2)] until arriving at the appropriate IAF.”

“Once cleared for the approach, pilots may descend in the TAA sector to the minimum altitude depicted within the defined area/subdivision, unless instructed otherwise by air traffic control. Pilots should plan their descent within the TAA to permit a normal descent from the IF/IAF to the FAF.” In this statement, the concept of a “minimum” altitude is present, but the MSA itself is not referenced. Let’s keep digging for a better answer.

So....What's The Answer?

The controller was correct: When we were cleared for the RNAV (GPS) Runway 1 approach at Emporia, we were authorized to descend to the MSA as long as we could determine we were within the circle (“defined area”) or sector (“subdivision”) of the charted MSA, which also defines the TAA. Since we were inbound from the southwest, this meant once we were within 30 nm of OVVOD, the IAF, we could (and should) descend to 3200 feet without further ATC clearance.

This goes counter to what we were taught in the days before GPS, when terrestrial navaids were the only game in town. (It’s also counter to what appears as the “correct” answer on any number of IFR quizzes.) Importantly, this exception only applies when flying an RNAV (in our case, GPS) approach, most likely because—as the citation from the IPH presented in Figure 1 implies—we no longer have to worry about “acceptable  navigation signal coverage.” Using ground-based navigation, a pilot might not be able to receive the navaid in use if he/she descends to the MSA prior to entering a published segment of that approach. With GPS, navaid reception is not a concern.

AIR TRAFFIC CONTROL

The FAA’s Order 7110.65, Air Traffic Control, often is referred to as “the Bible of ATC.” It’s the overall procedures document for controllers—and therefore pilots—when receiving ATC services. It can be a challenging read—not least because the latest iteration runs to 655 pages—but it does provide an approved, uniform set of guidelines for what’s expected from the controller’s point of view. Section 4-8 covers approach clearance procedures and provides a tremendous amount of technical detail on the subject, including this note under RNAV Application at the bottom of page 4-8-5:

NOTE—1. Aircraft that are within the lateral boundary of a TAA, and at or above the TAA minimum altitude, are established on the approach and may be issued an approach clearance without an altitude restriction.

Given that we’ve already learned that TAA and MSA are essentially interchangeable terms when operating with RNAV (GPS), this reinforces the policy that once within the TAA and cleared for the approach, we can (and are expected to) descend to the depicted MSA without needing to be on a published approach segment.

WHAT DID WE LEARN?

Put another way, when cleared for an RNAV approach, we should descend to the TAA’s minimum altitude, which is the MSA, as soon as we determine we are inside the defined area or subdivision of a TAA as published on the plate.

I have never encountered this before, although it’s likely controllers routinely simply direct pilots to descend or give the “maintain at or above” altitude limit until on the published approach to avoid confusion. 

PEER REVIEW

With something like this I wanted to get a professional opinion to back my research. I sent retired air traffic controller and current CFII John Foster the narrative above and asked if he feels I have interpreted it properly. John replied:

“Let me start by giving your customer an A+ for asking ATC to clarify a procedure that he/she was not 100-percent sure of. So many pilots are reluctant to verify ATC procedures for reasons I do not understand. Perhaps they don’t want to sound stupid, bother the controller, are afraid they will get chewed out, etc. But whenever the pilot has a doubt about the situation, verify it. So, A+ to the customer.

“I give the controller a B-. I say this because he was correct, you can descend, but not to an MSA. MSAs are ‘published for emergency use.’ They are not considered a published segment of an approach. The Aeronautical Information Manual (AIM) speaks to TAA approaches and TAA sectors as follows (emphasis added):”

“Think of a TAA sector as a very broad feeder route. A feeder route provides published course and altitude guidance from a feeder fix to the IAF. The TAA sector works the same, but there is no feeder ‘fix’ identified. Rather, it is replaced by the location of the aircraft itself within the TAA sector.”

ALWAYS LEARNING

I’m the first to admit I don’t know everything, and that I’m still a student pilot despite an ATP certificate, 4800 logged hours and over 30 years as a CFII. But this lesson about a critical nuance of RNAV approaches was a real surprise. In writing this, I run the risk that many pilots and controllers will say, “How did Tom not know that?” But I suspect most pilots will say, “I didn’t know that either.” Either way, both my student and I learned something new that day. If it’s news to you too, then I’m glad I wrote this.

Primary Sources

When I began researching the MSA clearance issue, it was very tempting to log onto an aviation forum or bulletin board—or even social media—and ask my question. In other words, let someone else do the work, and hope they know what they are doing. As someone who spends way too much time online and on social media, I know what sort of answers sometimes float around out there looking authoritative while they are anything but.

Do you have a question? Get into the books. Study resources like the FARs, your airplane’s Pilot’s Operating Handbook and its supplements, the AIM, Instrument Procedures Handbook, the Airplane Flying Handbook and other primary sources. As you answer your question, you’ll learn how to better answer future questions as well. Sure, it’s good to get a verifiably expert opinion like I did. But if you simply throw your question out there to the internet, you’re likely to get any number of conflicting answers with no good way to tell which is correct.