Tuesday, 24 April 2018

3 QUESTIONS TO ASK ABOUT WEATHER REPORTS

Acknowledgements: AIR FACTS (John Zimmerman)

Many discussions of aviation weather focus on tactical concerns, like how to interpret specific radar images, what an SLD icing chart shows, or why an MOS forecast is limited. Such topics are important because weather flying is fundamentally a very practical exercise, but they shouldn’t come at the expense of broader thinking. That starts with the familiar advice to get the big picture (fronts, lows, upper air charts) before diving into the particulars of a weather briefing.

Instead of saying, “the current METAR shows marginal VFR,” a wise pilot would suggest, “a strengthening low-pressure system is moving in quickly from the west, which is causing visibility to drop faster than forecast.” When you consider the big picture, you’re really creating a weather hypothesis – an overarching narrative that ties together the various weather reports.

Once you have a theory about the weather, it’s time to evaluate it, both before take-off and in flight. That means continually comparing your expectations to all available data. For better or for worse, “all available data” can be quite a lot these days, so it’s important to be structured about your research. Weather reports are not all developed the same way, and not all deserve equal attention.

Here are three questions to consider when comparing different weather products:

·       What is an observation and what is a forecast?
This may sound obvious, but many pilots trip up here. I’ve heard more than one pilot refer to the turbulence charts as if they were actual observations of in-flight turbulence, instead of the computer-generated models that they really are. The same goes for convection, icing, and visibility – understand whether you’re looking at actual conditions or a prediction about what might happen. This isn’t to suggest that forecasts are worthless; in fact, they’re getting noticeably better in recent years. When in doubt, though, an observation is generally worth more than a forecast. Don’t launch in the hopes that the TAF will magically come true; it may be time to update your weather hypothesis given the new data.

·       What is real time and what is delayed?
Especially when considering fast-moving weather events like a squall line, it’s critical to understand which weather products are in real-time, and which ones are delayed. Datalink radar, which most of us fly with these days, is incredibly valuable for long range planning. However, it is delayed by 5-15 minutes. That’s probably not an issue with lazy afternoon build-ups, but it could be a significant limitation in the middle of Kansas on a summer afternoon. Satellite imagery is even worse, with some maps only updating every 30 minutes, an eternity in most weather systems. It’s also worth noting the age of METARs. While technically not “real time,” some AWOS/ASOS systems report new weather every minute, compared to every hour for other airports. That’s a significant difference to consider, so be sure to check the time stamp of every METAR you read or listen to. What is truly real time? Onboard radar, if you’re lucky enough to have it on your airplane. This equipment can be finicky, but it offers priceless insights into the convective weather just off the nose. Other than radar, your eyes are the best real time weather detector – and they’re always on board. No matter what the XM Weather map shows, if it looks ugly it should be avoided. Just like an observation should probably get more weight than a forecast, a real time data source should override a delayed one.

·       What is objective and what is subjective?
Finally, separate objective weather products that report “just the facts” from more subjective ones that are subject to biases. For example, visibility is an objective value that is measured by calibrated instruments. While sensors can (and do) lie, most of the time 1 mile of visibility really means 1 mile. A PIREP, on the other hand, is far from objective. What feels like moderate or severe turbulence in a Cessna 152 may be reported as light turbulence by a Boeing 767 crew. Even among similar airplanes, the phase of flight can have a significant effect on what gets reported: icing often seems heavier during a slow climb than during a rapid descent.
I find PIREPs to be quite valuable, especially for determining where the ice and cloud tops are, but they must be understood in context. Consider the type of airplane, the phase of flight, the age of the report, and the broader weather picture before you accept it as fact. The number of PIREPS can also be a key indicator of accuracy (nine reports of moderate turbulence probably mean more than a single one), but don’t fall into the “no PIREPs means good weather” trap either. There are usually no PIREPs in a hurricane; that’s not because there is no weather to report!

THE GOLDEN RULE:

The ever-increasing variety of weather forecasts, from icing probability charts to forecast radar images, is a real benefit for pilots. They aren’t to be feared or ignored simply because a computer spit out the result. Just remember to keep the right perspective about our job as pilots: while weather forecasting is a science, weather flying is not. Online weather maps and datalink radar are part of the in-flight decision-making process, but the most powerful tools are probably your eyes and your gut.

In flight, Richard Collins’s familiar rule is the one to remember: What you see is what you get. No matter what your theory was before take-off, and no matter what the forecast suggests, you have to deal with the weather you find in the atmosphere around your airplane. That argues for using observations, real time weather sources and objective data whenever possible.

FLY SAFE!

Monday, 23 April 2018

PRECISION TOUCH-DOWN

Acknowledgements: Thomas P. Turner (Mastery Flight Training Inc.)

(Ed. Note: Another great lesson from the MASTER!)

“The engine had burned for 35 seconds and during that time the airplane had accelerated to Mach 2.2 in the climb. Jack [the pilot] peaked out at 78,400 feet altitude during the wingover turn back to Delamar. He made a nice approach pattern, but he was high on energy. Jack was an old Navy pilot like me, and we both carried an extra 5 knots of airspeed in the approach for each of our kids to ensure wedid not stall the aircraft. Trouble was, Jack had eight kids! 

He landed long and ran off the edge of the [dry] lake [bed] about 500 feet in the sagebrush before stopping. It did not hurt the airplane and Jack did not let it affect his ego! After the post-flight debriefing, someone asked Jack how long the lakebed runway was. Jack’s answer was, “Three miles with a 500-foot overrun.”

Touching down with precisionon a defined spot on the runway or landing surface, is an exercise in mastery and command of the aircraft. It’s as much an art as it is science to have the aircraft meet the earth exactly where you want. It takes concentration and planning, experience and currency. It requires the pilot read the aircraft, and the weather, and make constant, subtle changes to react to changes brought on by the environment, the pilot’s own actions, and perhaps most elusively, the pilot’s perception of the need for those changes and how to respond.

Yet just when most pilots hone these skills to a sharp edge, we tend to let them fall into atrophy. In a world of mile- (or miles)-log runways, precision touchdowns seem to lose importance. Unless you’re a bush pilot or practicing for an upcoming check-ride, it’s easy to believe it’s just not all that important to consistently put the airplane down on a precise spot or even within a specific touchdown zone.

Meanwhilelike the X-15 pilots in the excerpt above, many pilots develop an enhanced fear of stalling the airplane on final approach. It’s as if all that time practicing stall recognition and recovery in the process of earning pilot certificates is aimed at making us afraid of stalls, when the purpose is to make us aware of Angle of Attack, and how to use it for maximum performance and accuracy during take-offs and landings.

Furtherit’s common and accepted practice to add some additional airspeed on final when approaching in gusty surface winds. The Industry Best Practice is to add one-half of the gust factor. This means to take the difference between the steady wind speed and the speed of maximum wind gusts, divide that difference by two, and add that value to your normal (i.e., no gusts) final approach speed.
The result is usually not nearly as significant as you might think. For example, as I write this the reported wind at my home ‘drome is 19G25. There is a six-knot difference between the steady wind speed (19 knots) and the maximum gust (25 knots). One-half of this gust factor is three knots, which I’ll add to my final approach reference speed.  That’s only three knots to add to my 78-knot reference speed passing through 50 feet Above Ground Level.

Do you fly every final approach within a range of three knots?

Thinking in terms of the gust (25 knots!) and not the gust factor (only six knots) might inspire me to add a lot more to my final approach reference speed than the situation calls for.  
So what happens when you add a few knots for the wife and kids, or because you overestimate the adjustment for a gusty surface wind, or simply because you no longer fly as precisely as you should… and that you proved you could, on at least one check-ride flight when you were just beginning to be a pilot? 

Two issues are directly affected by the precision of your airspeed on final approach:
1.     RUNWAY OVERRUN. Approach fast and you will likely land long. Land long and you may not have the runway length remaining to come to a stop (like that X-15 pilot). Runway overruns (going off the far end of the runway otherwise under control) are a common mishap scenario. A variation is the pilot who realizes his/her mistake and decides—too late—to add power and go around, only to (a) overrun the runway at full power, (b) collide with obstacles off the far end of the runway, or (c)stall the airplane in an overzealous attempt to pull up when outcome (a) or (b) appears imminent.
2.     PILOT-INDUCED OSCILLATION (PIO). Approach fast and force the airplane onto the runway in an attempt to avoid landing long, and it’s likely the airplane will bounce. From there, it will take skill and discipline to avoid entering a pilot-induced oscillation while you try to “catch up” with controlling the airplane. 

As you come down final approach, consciously evaluate whether you are on speedin configuration (flaps, landing gear as applicable), on glide-path to your identified touchdown zone, and aligned with the runway centreline. Crossing the threshold, or the last obstacle, or the beginning of the landing area (if it’s not a purpose-built aircraft landing surface), if you are not correct in all four of these criteria then go around immediately. Don’t try to salvage the landing if too fast (or too slow), out of landing configuration, above or below glide-path, or out of alignment with the runway.

Use an aim point to define a Touchdown Zone. If you’ll land beyond the touchdown zone you are in The Go-Around Zone. As the name implies, go around without hesitation.

Landing an airplane precisely is an exercise in aircraft control. You may never need to get the maximum landing performance out of your aircraft…. until you fly into a high density altitude airport, or have to make a precautionary landing at a short strip, or have to fit a crippled airplane into a farmer’s field after engine failure or an inflight fire forces you to make an off-airport landing. 

If that time comes, you need to be able to be able to fly to the high level of precision you exhibited on your last check-ride. In an emergency there isn’t time to practice on the way down.

All aircraft performance targets are defined by an indicated airspeed (in the absence of military/jet-quality Angle of Attack indicators). Make it a matter of pride to know and hit your airspeed targets in all phases of flight. Not only will you hone your skills as master and commander of your aircraft, you’ll also:
·       get the maximum and most efficient performance all of the time
·       avoid the depressingly common runway overruns, delayed go-arounds and PIOs
·       be as prepared as possible when today is the day you need to respond to an emergency

FLY SAFE!