June 25, 2013
By Dan Namowitz
Slipping into the cloud bases on an IFR departure, you recoil at the sight of ice forming on leading edges as you trim for the climb and turn to the assigned heading.
For most instrument pilots, two questions will immediately cry out for any attention that can be spared from the high workload of a departure climb into immediate IMC. “What’s the outside air temperature?” and “Where are the tops?”
Glance at a gauge to glean the outside air temperature. But figuring out when you’ll pop out on top is more uncertain—not a troubling thought until the ice appears. Now as the climb proceeds and the temperature—still in the sweet spot for icing—holds steady, it’s tempting to wonder if there was more information available about the position of the tops.
The answer is, probably not. There was a big-picture guesstimate offered in the area forecast: BKN010-020 BKN080 TOPS 120. OCNL VIS 3-5SM BR. ISOL –SHRA. But your briefing contained no pireps about tops or icing.
After departure, you heard an arriving heavy aircraft request an ILS approach because of “weather between us and the field.” That didn’t add much detail, but it did suggest that the jet was descending in visual conditions while expecting to be on gauges for the approach.
With all the detailed information that is available to pilots for weather briefings, cloud tops remain largely in the realm of far-reaching FAs and extremely localized UAs. Even the IFR clearances specifically designed to deliver a flight to clear air above clouds can contain a critical caveat:
“Pilots desiring to climb through a cloud, haze, smoke, or other meteorological formation and then either cancel their IFR flight plan or operate VFR-on-top may request a climb to VFR-on-top. The ATC authorization contains a top report (or a statement that no top report is available) and a request to report upon reaching VFR-on-top. Additionally, the ATC authorization may contain a clearance limit, routing, and an alternative clearance if VFR-on-top is not reached by a specified altitude,” explains the Instrument Flying Handbook.
That’s of some consolation for a pilot who wonders whether something was overlooked during planning—but of no immediate value when ice, turbulence, or an equipment malfunction makes a tops report the only tidbit of information that you really, really, want to hear.
Dan Namowitz is an aviation writer and flight instructor. He has been a pilot since 1985 and an instructor since 1990.
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