The MSA on this LOC/DME approach to Aspen, Colorado, is centered on the Red Table (DBL) VOR/DME. The final approach segment minimum altitude to the Jargu intersection is 13,400 feet—just 300 feet above the MSA segment in that area.
Often overlooked, yet important approach plate items
When it’s time to shoot an instrument approach, most of our attention is focused on the lateral and vertical approach path depictions. Then comes a good look at the landing minimums, the navaids being used, the runway diagram, and the missed approach procedure. The ATIS or AWOS frequency should already have been checked, so there’s a good general sense of where—or whether—you’ll break out of the clag on the final approach course. It’s all part of the approach briefing, which should be performed well in advance of every approach.
Most instructors teach students to read the approach plate from top to bottom, so that a routine is established. It also helps to talk aloud as you go through each item on the plate; this helps you remember and reinforce the procedural details.
Typically, one item on the approach plate is briefly acknowledged, and then our scans tend to move quickly along. This is the minimum safe altitude (MSA), or minimum sector altitude in International Civil Aviation Organization parlance. The MSA symbol, which appears at the fringes of the approach planview, shows the altitudes providing 1,000 feet of clearance from terrain or obstacles within prescribed radii and distances from a defined navaid or fix. Some assume that the MSA depiction is centered on the airport targeted in the approach. Not necessarily!!
On approach plates showing ILS, VOR, LDA, SDF, or NDB approaches, the MSA symbol is a circle, with the defining navaid’s icon in the center. Extending radially from the center are tracks designed both to carve up the areas of differing minimum altitude, and to help orient pilots to their relative position.
On RNAV (GPS) and other approaches using the T-style track arrays from initial approach fixes, the MSA segments can be pie-shaped or half-circles rather than circular. On approaches to airports in mountainous regions, there can be more than one published MSA. That’s because terrain elevations may vary greatly within the charted area.
The standard guidance on MSAs is pretty thin. MSAs are not part of the approach procedure, even though the navaids or fixes that define them typically are located on or near approach paths. Instructors, like the FAA, simply say that MSAs are published for “emergency use.”
This raises the question: When might you make use of an MSA’s information? One way an MSA might come in very handy is if you’re on an approach and you experience a failure of either the approach’s navaid or your airplane’s navigation receiver, or a complete electrical failure. With no course guidance, the best alternative might be to climb to an altitude at or above the MSA in your sector, following a track that corresponds as closely as possible to the missed approach procedure. At least you’ll know you’ll clear terrain and obstacles.
MSAs also may give you an out if you find yourself lost or disoriented at night in mountainous terrain, and without terrain displays or ground proximity warning equipment. They could help during a botched approach as well, if there is no radar coverage and you’ve let your course deviation indicator peg itself off-scale. They can also be used to compare against your assigned altitude, should you get the feeling you’re too low. ATC uses minimum vectoring altitudes, so this shouldn’t be an issue, but questioning an altitude that’s lower than the MSA won’t hurt—and might alert a less-than-vigilant controller.
Just remember this: While MSAs do guarantee clearance from terrain and obstacles within their defined boundaries, they do not guarantee nav reception.
What about you? Have you ever had to make use of an MSA?
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Illustration by Kevin Hand
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