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When you fly from west to east, sometimes your route heads west to avoid obstacles or to clear class B or C airspace.

According to hemispheric rule, let's pretend I selected 7500 feet for VFR to the east. En route to a destination with flight following, when I change heading to the west and the route to the west takes about 30 mins, can I remain the altitude until I get a new instruction from ATC? Or, should I request descent/climb and follow the hemispheric rule?

The destination and the post-take-off route are to the east, but when most of the route is to the west, it makes me confusing to select a proper altitude.

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  • $\begingroup$ Are you in controlled airspace? $\endgroup$ – J. Hougaard Aug 25 at 11:14
  • $\begingroup$ Your mention of class B or C airspace, and Flight Following, makes me think you're talking about conditions in the US. Is that a correct assumption? $\endgroup$ – a CVn Aug 25 at 11:57
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    $\begingroup$ Yes, I'm talking about conditions in the US. In this case you don't need to think about class B or C. I'm just wondering the proper procedure when I change heading $\endgroup$ – gusdyd88 Aug 25 at 17:53
  • $\begingroup$ Somewhat related $\endgroup$ – Pondlife Aug 25 at 20:19
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First, your question implies you have flight following. So there would really be no need to avoid class C or B airspace since ATC would simply fly you through them or make their own decision to ask you to go around, over, or under them.

ATC should know to assign a different altitude when you change from east to west or vice versa, but if they do not, yes, you should request an appropriate altitude for the heading that will keep you in VMC conditions.

Keep in mind, that if you are told to "resume own navigation" or "proceed on course", they are allowing you to change your heading and altitude as you please, so you wouldn't need to ask for special permission to change it, and in that case, just change to an appropriate altitude that will keep you in VMC. No need to say anything; if ATC decides they don't like what you're doing, they would give you a new instruction.

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  • $\begingroup$ When I request flight following, if there is two or more altitude I planned en route due to weather or terrain, etc..which altitude should I say? For example, the initial altitude I fly is 5500, from middle point of the route, I'll climb to 7500, and then arrive at destination. $\endgroup$ – gusdyd88 Aug 25 at 18:03
  • $\begingroup$ When you request flight following, tell them your current altitude. If you're climbing, indicate your current altitude you're passing and your target altitude. If they assign one and you want to change it, you can ask. $\endgroup$ – Ryan Mortensen Aug 25 at 19:39
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    $\begingroup$ ATC can certainly give you instructions if they need to but flight following is usually advisory only. It's good to tell them that you're changing altitude in particular however in most cases you don't need their permission to actually do it. I think that's probably what you intended in your answer, but the second paragraph in particular makes FF sound more 'formal' than it really is. That may be just me though :-) $\endgroup$ – Pondlife Aug 25 at 20:18
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    $\begingroup$ Remaining clear of Class B airspace without an explicit clearance to enter that airspace is always the responsibility of the pilot operating under VFR, regardless of whether or not he or she is receiving flight following or is otherwise in communication with ATC. When under flight following, ATC may provide one with a clearance into Class B airspace, or may request that the pilot remain clear, but it is still the pilot's responsibility to ensure regulatory compliance. $\endgroup$ – J Walters Aug 26 at 2:17
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If you are on VFR Flight Following you usually don’t need to ask permission to change altitudes. The exception would be if you are given an altitude to fly from ATC. For example, last week I was flying west from Corona and approaching Burbank’s airspace. While climbing through 4,000' I was given an altitude restriction of “At or below 5,000'”. ATC had me fly over Burbank’s Class C altitude (4,800') but wanted to keep me below the departing traffic. I could see a big jet pass me and once it did I was told to “resume own navigation”. On my initial call I had indicated that I was going to fly home at 6,500' so I climbed to that altitude. I could fly at any appropriate altitude, e.g. 4,500', 6,500', 8,500' etc. but given how busy the airspace is and the expectation of ATC that I would remain at 6,500' I would not change altitude unless I first arranged to do so with ATC.

On the flight into Corona, at around 15 miles from the airport, I was given instructions to fly at or below 3,000'—presumably to avoid traffic departing Ontario. There was no need to inform ATC that I was leaving 3,000' when I had the airport in sight and began my descent.

On the other hand, once I got past Ventura, the traffic volume was much lower so I wouldn’t necessarily talk to ATC if I wanted to climb to go over a mountain or avoid a cloud.

As a general rule, when you begin your descent to land ATC can figure it out. In many cases the beginning of the descent corresponds with picking up the ATIS. Since ATC likes to know that you have the ATIS I will usually combine the descent and ATIS call in one transmission.

In your specific example, since you will be flying at the wrong altitude for 30 minutes, you should either climb or descend—unless your current altitude was assigned by ATC.

FYI, in SoCal when ATC says “At or below 5,000'” they really mean “at exactly 5,000'”.

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    $\begingroup$ "in SoCal when ATC says “At or below 5,000'” they really mean “at exactly 5,000'”." Maybe it's just me, but if ATC wants to say "maintain 5,000", IMO they should say "maintain 5,000". Alternatively, "5,000 or below, remain outside of Class C" (or whatever the exact phraseology would be) which, in your example, would correspond to effectively a block altitude of 4800-5000, thus making 5000 a convenient, nice, round number. Maybe this is just another one of those idiosyncrasies that differentiate US phraseology from ICAO phraseology... $\endgroup$ – a CVn Aug 26 at 5:55

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