It’s way too early to know what happened to cause early July’s mid-air collision between a Cessna 150 and a U.S. Air Force F-16C near Moncks Corner, S.C.
The accident is being investigated by the NTSB, but it’s likely the pilots involved were where they were supposed to be, doing nothing unusual. Both aboard the Cessna died, while the F-16’s pilot safely ejected and reportedly was uninjured. Both airplanes were destroyed.
Regardless of the investigation’s outcome, it’s not too early to highlight some things about military flight operations we all should know, but sometimes omit from our flight planning. We know about military operations areas (MOAs) and restricted areas, for example, but it appears the collision occurred outside such airspace.
Media reports mention the F-16 pilot was engaged in some form of instrument training. I know next to nothing about F-16s, but it’s unlikely its pilot was shooting approaches under the hood in a single-seat fighter. Instead, it may have been on a published military training route (MTR), which are easy for civilian pilots to ignore. In fact, an instrument MTR is charted very near where the the two airplanes apparently collided.
All kinds of stuff goes on in the U.S. military’s special use airspace and the vast majority of it is unhealthy to civilian pilots, unless you enjoy things like live-fire exercises, bombing practice and mock dogfighting up close and personal. An MTR, meanwhile, is for conducting low-altitude, high-speed training. How low, and how fast?
Below 10,000 feet and in excess of 250 knots is the official word, but an MTR can be flown below 1,500 feet AGL and at more than 300 knots, perhaps a lot more. At those speeds and altitudes, no one has much time to react, or many places to go when they do.
The Aeronautical Information Manual sums it up in a classic understatement: “The required maneuvers and high speeds are such that they may occasionally make the see-and-avoid aspect of VFR flight more difficult without increased vigilance….”
And since they’re routes rather areas, an aircraft using one literally is a moving target. Each MTR can be up to 16 nm wide — eight nm either side of the centerline — and they come in two flavors, visual and instrument, and are used both day and night. A visual MTR, or VR, is the type extending below 1,500 feet AGL — to as low as 100 feet — while instrument routes, IRs, use that same 1,500 feet AGL as a minimum altitude.
Charting of MTRs can be deceptive. Instead of a vivid splash of color telling pilots “here be fast-moving dragons,” a relatively narrow, gray line is used on sectionals and a brown one on low-altitude en route charts.
Figure 1 depicts MTRs throughout the Continental U.S. — outlined in red — courtesy the See and Avoid website (SeeAndAvoid.org), which is jointly funded and operated by the FAA and the Air National Guard.
Figures 2 and 3 depict how MTRs are charted on sectionals and low-altitude en route charts, respectively, zoomed in on Moncks Corner.
If one zooms in even more on the airspace near the Berkeley County Airport (KMKS) in Moncks Corner, as in Figure 4, an MTR identification — IR18 — is visible within the smaller yellow circle.
The charting denotes an instrument route and the arrow indicates it’s designed to be flown from the south to the north. In other words, if we’re departing KMKS to the east, it likely won’t do us much good to look for high-speed military traffic to our left; it’ll be coming from the right side of the aircraft, perhaps from behind us.
The larger yellow circle of Figure 4 highlights two additional points. The first is how IR18’s charting is partially overlaid by a divided highway, also depicted running roughly north-south right next to the KMKS airport.
The second point is how close IR18 is to KMKS. In other words and given an MTR’s maximum width of 16 nm, the possibility exists of a military aircraft blowing through the VFR traffic pattern at the Berkeley County Airport, and presumably others, at more than 300 knots.
Even if you have a current sectional, there’s no guarantee it accurately depicts an MTR. That’s because MTRs are revised on a 56-day cycle, while new sectionals come out every six months.
According to the FAA Aeronautical Chart User’s Guide, pilots are “cautioned and advised” to check with Flight Service for dimensions and status of MTRs along a proposed route. The User’s Guide also advises that changes in charted MTRs will be “indicated in the Aeronautical Chart Bulletin of the Airport/Facility Directory.”
On low-altitude en route (IFR) charts, all MTRs except those VRs entirely below 1,500 feet AGL are depicted. Since these charts are updated every 56 days, it’s likely they show the present MTR alignment.
Also, the depictions on low-altitude en route charts allow users to distinguish between narrow and wider MTRs: Those with a total width of five nm or less are shown by a 0.02-inch line, while wider ones use a 0.035-inch line. That distinction really is important only if you’re using a paper chart, since electronic charting allows us to zoom in and out, making the line’s width difficult to determine.
At this point, it’s not at all clear the F-16 was using IR18 when the mid-air occurred or if it was on some other sort of training mission. It’s also not clear at what altitude the collision occurred, whether ATC was involved in monitoring either airplane, or if the 150 even had a working transponder.
It is clear that MTRs can be an oft-ignored factor in our flight planning, however, and it might be a good idea to re-think how and where we look for traffic while airborne. I know I will.