Aviation In Canada

Saturday, January 29, 2005

Block Altitudes

I mentioned a few days ago the concept of "Block Altitudes". I hope to fill that gap now.

Sometimes a pilot may have difficulty maintaining altitude due to weather conditions or some other reason. Perhaps strong turbulence is becoming a problem, you're riding the tops of cloud in and out of icing, whatever. An option open to pilots is a block altitude. ATC doesn't provide clearances to aircraft in blocks of altitudes without a pilot request. The request for the block normally must be accompanied by the reason for the request. This is more of a rule ATC is required to follow, rather than just ATC being nosey. Controllers have a number of conditions they are supposed to meet before approving a block altitude. They have to know what the reason is, and when you can return to a "hard altitude". This last one is difficult in some circumstances, since a pilot or a controller likely won't know when icing conditions will end. They also have to see you meet certain requirements that you may not even be aware of.

Your flight must be a training flight, flight checking a NAVAID (and no, the average pilot can't qualify for this one), or you must require it for fuel reasons, turbulence or icing. This is the same as the rules for an altitude inappropriate for direction of flight (5,000 feet for a westbound aircraft).

The phraseology ATC will use for assigning a block altitude will sound something like, "Alpha Bravo Charlie, maintain the block from six thousand to eight thousand." Some will say, "... maintain six blocking eight thousand," but it means the same thing.

When a block altitude is no longer required, a pilot should endeavor to maintain an appropriate altitude for direction of flight within the assigned block, or request a different altitude, and advise ATC the block is no longer required. ATC should then issue a clearance to maintain the desired altitude, implicitly cancelling the approval for the block.