5 (Refer to FAA-CT-8080-2G, Figure 59, area 2.) The chart shows a gray line with "VR1667, VR1617, VR1638, and VR1668." Could this area present a hazard to the operations of a small UA?
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These gray lines on the VFR charts indicate Military Training Routes (MTR).

§91.117 'Aircraft speed.'
(a) Unless otherwise authorized by the Administrator, no person may operate an aircraft below 10,000 feet
MSL at an indicated airspeed of more than 250 knots (288 m.p.h.).

MTR, or Military Training routes are low-altitude training routes generally below 10,000' Mean Sea Level
(MSL) for speeds in excess of 250 knots.
MTRs are depicted as thin, light gray lines on the sectional. Each has its own identification, and the identifier has two parts. "VR" means that pilots flying the routes will be flying under visual flight rules. "IR" means the pilots will be flying under instrument flight rules. The second part of the identifier is either a three or a four-digit number. Four digits means the route will be flown at or below 1500 feet AGL. A three-digit number means the route will be flown both below and above 1500 feet AGL. Thus, on the chart section below, VR-1267 means a training route flown under VFR at a relatively low level. IR-218 would be a route flown under IFR conditions at any level. A jet fighter traveling toward you at over 300 miles per hour can be very hard to see, so it's a great idea to keep any local MTRs fixed in the back of your mind, and to be especially alert when operating near an MTR.
Arrows are shown to indicate the direction of flight along the route. MTRs can vary in width from 4 to 16 miles. The width of the route determines the width of the line that is plotted on the chart.  Route segments with a width of 5 NM or less, both sides of the centerline, are shown by a .02” line.  Route segments with a width greater than 5 NM, either or both sides of the centerline, are shown by a .035” line.

It is very subtle and without a measuring stick (engineering scale) you would be challenged to identify one by itself. Here are two MTR's on the Arizona Sectional Chart, VR1267-1268 and IR218 that show the difference. IR218 is the thinner line of the two shown here.
This is correct.
Military flights along VR routes may fly at any altitude.  A four-digit route identifier means that no part of that route segment will be over 1500 ft AGL.  But flights not in a MOA (Military Operating Area) are constrained to ยง91.119 - Minimum Safe Altitudes.  This means they should be flying between 500 and 1500 ft AGL, well above the ceiling for drones (400 ft AGL).
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