How the rule helps assure separation
The rule on VFR cruising altitudes, found in Federal Aviation Regulation 91.159, may be one of those rules. It requires that you identify your heading and then fly at a certain altitude based on that heading. It helps pilots meet their responsibility to "see and avoid" other air traffic. That is, when VFR aircraft are required to operate at certain altitudes when traveling in opposing directions, pilots are better able to spot traffic and take action to avoid any traffic that could pose a collision risk. The rule helps you to see and avoid other aircraft by allowing you to generally anticipate where other aircraft may be in the sky.
As it is relevant to our discussion, the rule states that "each person operating an aircraft under VFR in level cruising flight more than 3,000 feet above the surface shall maintain the appropriate altitude or flight level prescribed below, unless otherwise authorized by ATC:
"When operating below 18,000 feet msl and --
"(1) On a magnetic course of zero degrees through 179 degrees, any odd thousand foot msl altitude plus 500 feet (such as 3,500, 5,500, or 7,500); or
"(2) On a magnetic course of 180 degrees through 359 degrees, any even thousand foot msl altitude plus 500 feet (such as 4,500, 6,500, or 8,500)."
One way to paraphrase this rule is to say that when the ground track of the VFR pilot's aircraft is in an easterly direction, that aircraft should be at an odd altitude plus 500 feet, e.g., 5,500 feet. When the ground track of the VFR pilot's aircraft is in a westerly direction, the aircraft should be at an even altitude plus 500 feet, e.g., 4,500 feet. I was taught to remember this by saying that east is odd, but west is so much odder as to be even, and then add 500 feet. Another memory aid is WEEO, for west even, east odd -- again, plus 500 feet.
We must emphasize that the requirement to comply with the VFR cruising altitudes only applies to those VFR flights conducted higher than 3,000 feet above ground level (agl). Below 3,000 feet agl, other VFR or IFR aircraft could be at any altitude that potentially may conflict with your flight path. Second, your VFR cruising altitude will be determined according to your altimeter as set to mean sea level (msl). You must have the appropriate altimeter setting entered into your altimeter to make sure you are operating at the correct altitude. FAR 91.121 states that your altimeter must be set to the current reported altimeter setting of a station along the route and within 100 nautical miles of your aircraft, or if there is no station within this area, the current reported altimeter setting of an appropriate available station. Third, this rule requires VFR traffic to operate at even or odd altitudes plus 500 feet, while IFR traffic is generally assigned to fly the cardinal altitudes -- 2,000, 3,000, 4,000, 5,000, and so on. Therefore, you shouldn't count on there being a 1,000-foot safety separation between aircraft because that safety margin may only be 500 feet at most. And, any traffic that is climbing or descending could cross through your altitude.
So, the rule does make sense. The rule provides that traffic operating above 3,000 feet agl, traveling in opposite directions, be separated by a margin of airspace. When you're flying at the appropriate VFR altitude, any opposing VFR or IFR traffic should be above, below, or crossing through your altitude but should not be cruising at your altitude.
While the VFR cruising altitude rule may assist you in detecting opposing traffic, it may not help you see and avoid aircraft that may be traveling in the same easterly or westerly direction that you are traveling and, thus, at the same altitude. In that circumstance, you may be overtaking another aircraft or another aircraft may be overtaking you.
This rule works in conjunction with other regulations to keep aircraft safely separated. Still, it does not alleviate your responsibility to maintain a proper scan outside your aircraft in order to see and avoid any traffic. Keep your head on a swivel.
Kathy Yodice is an attorney with Yodice Associates in Washington, D.C., which provides legal counsel to AOPA and administers AOPA's legal services plan. She is an instrument-rated private pilot.
Related Articles
