|Wind Shear, UFO *
From The South Ramp --Hank Bruckner May 2004
Break in the Clouds
Summer is just around the corner, capping off the longest and wettest winter in recent memory. Spring got bypassed entirely, mostly by passing shear lines. Just what is a “shear line”? Enough of them have come through here to warrant a closer look. They are lines or narrow zones across which there is an abrupt change in the horizontal wind component parallel to this line. A shear line is an area of directional wind confluence along the tail end of a surface front. Not only that, it also lacks the baroclinicity/density discontinuity of surface fronts, and I’m sure you all know what that means, so I won’t bore you with the details.
A front is the zone between two air masses of different density and temperature, whereas a shear line refers to the airflow. So, a shear line isn’t a front but is frequently associated with one and can apparently behave like one, at least as far as rain, mist, low ceilings, junky visibility and unruly winds are concerned.
So, you very well might ask, what? I like my meteorology simple (along with most other things). For example, if I’m told that a front is approaching, I know to expect some inclement weather and a wind direction change as it passes. But, tell me a shear line is coming, and I really don’t know what to expect. This past winter had shear lines that did excellent impersonations of fronts and made flying conditions a true challenge and others that passed almost unnoticed (not too many of the latter). A “weak shear line” passed through a few days ago that left Moloka'i IFR most of the day as it lingered over that island on its way southeast. Bottom line? I’m ready for summer flying weather.
February and March usually bring some strong trades (above 25 knots) as the controlling high-pressure systems develop a tight gradient. This year, with our elongated winter, that didn’t occur much until April. On one day, my return leg from Moloka'i at 1,500’ featured a ground speed of 203 knots on both the DME and GPS, with an indicated air speed of 162 about mid way across the Ka’iwi Channel. Winds at Moloka'i were listed as gusting to near 30 and at Honolulu slightly less. The winds aloft forecast had the winds at 25 knots at 3,000’. So, where did the 40+ knot winds come from?
The channels between the islands can act as venturis given the right combination of wind direction and velocity, and I suspect that mid-channel flow acceleration was just that. Makes the eastbound flight very slow and the westbound one quite fast. Naturally, you never gain as much in the tailwind as you lost with the headwind.
Local knowledge really counts when the winds blow here. As the wind flows over and around bits of island, it will change direction and speed in ways that vary significantly with the direction of the inbound airflow. A difference of two or three degrees can have a huge impact on where eddies form and where you may encounter shears—updrafts, downdrafts, and turbulence.
You can expect downdrafts on the lee side of a ridge. The intensity of the downdraft is related to the velocity of the flow. It is not uncommon to encounter a downdraft that matches or exceeds the climb performance of your aircraft. Most of us who have flown here for a while have experienced that to some degree or another. A downdraft was reportedly a major factor in the recent crash of the Piper on Mauna Loa’s western flank.
A downdraft is a downward moving flow of air that can originate from a number of sources, such as the flow of wind over a ridge (common in Hawai’i). Downdrafts are also present in thunderstorms, where the precipitation forces a downward rush of air—in severe form known as a microburst. The myth is that a downdraft won’t extend all the way to the surface, because it will rebound as it strikes the surface, and form some sort of a cushion effect. Several accidents would indicate otherwise. Even if the airflow does rebound, the aircraft caught in it likely won’t.
So what to do if you get caught in one? Each situation has its own dynamics, of course, but the first thing is to recognize it for what it is, followed by an assessment of its severity. The readiest indication is your VSI. Pitch+Power=Performance is true in a relative sense only, within an air mass. If the entire air mass is either rising or descending, so will you, within it, and you won’t be seeing the performance you would expect from your combination of pitch and power. You may be climbing at 1,000 feet per minute, but if the air mass you are in is descending at 1,200 FPM, your VSI will point down at 200 FPM.
If the VSI shows you can’t climb faster than the air mass is descending, then you must get out of that flow. Mountain flying texts recommend approaching a ridge from the lee side at a 45-degree angle rather than straight on, so that you can more easily make the turn away from any nasty downflow.
When the wind blows, try to visualize the flow. Over the ocean, you can often see where the airflow changes reflected on the surface. Update your mental picture with what the airplane is telling you about the air mass you are flying in, and have an escape route in mind in case you need it.
Ultimate Goal *
There is an exclusive club in aviation that we can all aspire to join, but few do. It is the United Flying Octogenarians, and we are fortunate to have one recently qualified member among us: John Gleeson. To join, you must be between 80 and 90, have a current medical certificate, and have flown as PIC since your 80th birthday. There are about 400 members nationwide, including John. Incidentally, Willy Schauer just celebrated his 80th too! Congratulations to both. There is the possibility of starting a UFO Chapter in Hawaii. Contact John Gleeson 942-1896, email@example.com for an application
Now here’s the down side. If you are 80 years old, even though you have a valid airman’s certificate and medical certificate, the AOPA Insurance Agency will not write you a policy. It seems to me that AOPA, of all organizations, would not be associated with such blatant age discrimination.
Up and Running
By now you will have undoubtedly noticed a new presence in our island skies. A fleet of Beech 99s and 1900s belonging to Alpine Air have begun flying the Interisland mail. In about a week, Alpine brought in 11 aircraft and began operations throughout our island chain. The logistics were daunting. Just finding a place to park and operate that many aircraft at HNL was a challenge.
Alpine flies mostly at night, but you’ll see some of them around during the day as well. The addition of new planes and pilots to our skies is reason to remain ever watchful. As mesmerizing as that new electronic display may be, it is even more important to keep your eyes outside the cockpit and your ears and mind open to what’s going on around you.
Corrosion never sleeps, especially in our oxidation-friendly environment. It is insidious and destructive. If your airplane has been sitting on a ramp for a while, you will have corrosion—probably more than you imagined. It isn’t until your airplane is stripped for painting that the extent of the corrosion becomes evident. It is neither a simple or inexpensive process to deal with, but deal with it you must.
Jim Straube moved his aircraft painting business to Hangar 110 at Kalaeloa. He now can handle almost any size of aircraft in his much larger facility. Jim and his crew did virtually all the really good-looking paint jobs you see in our skies.
St. Ex Wreck Located
“He passed his fingers along a steel rib of the plane and felt the life that flowed in it; the metal did not vibrate, yet it was alive. The engine’s five-hundred horsepower bred in its texture a very gentle current. Once again, the pilot in full flight experienced neither giddiness nor any thrill; only the mystery of metal turned to living flesh.” That quote (which I’ve used before) is from Night Flight by Antoine de Saint-Exupéry. The wreckage of Saint- Exupéry’s P-38 was found last month in waters of Marseille. Saint- Exupéry was on a photo recce mission over the Mediterranean in 1944 when he just failed to return, sparking an enduring mystery. The location of the wreckage only solves part of the mystery. Why he crashed is still unknown, and likely will remain so.
Saint-Ex, as he was often called, was best known for his book, The Little Prince. Wind, Sand, and Stars, and Night Flight are among his best-known aviation books. As a pioneer aviator, he opened mail routes in Africa and South America. He was a close friend of Anne Morrow Lindbergh. Whether you consider him a flier who wrote or a writer who flew, Saint-Exupéry is one of the icons of aviation literature.
Sadly, we won’t be taking our pilgrimage to Oshkosh this year. The new wing for my CAP-10 has consumed enough resources for an around-the-world cruise in the Concorde (were it still flying). I’ll miss the annual immersion in all things aviation, of course, but most especially, the good friends—old and new—we share the experience with. If you are going, take notes and pictures and write us a feature for the ‘Scoop.
The state DoT held another of their periodic GA Forum sessions on March 18th. The state and federal government were well represented. Only five GA folks showed up, which is, to say the least, disheartening. As with past meetings, we reviewed the status of issues and raised some others. There actually has been some progress in certain areas and many others remain “open”. The DoT mailed a list of all the old and new issues and their status to all or most of the GA pilots and owners, so I won’t revisit the details here. Morris Tamanaha, the state General Aviation Officer, conducted the meeting and has done a lot of work on all our behalf. Mahalo.
Here’s the thing. We all complain about many of the things that are worth complaining about (and maybe some that are not), and the DoT, partly at GACH insistence, came up with the GA Forum as a vehicle to air the issues that are important to us and let us vent a little. These meetings are in the evening and all the state and federal representatives present were giving us their own time. The least we can do is attend. The next one is scheduled for September 16th, from 6:30 pm to 9:00 pm at the Airport Conference Center on the seventh floor of the Interisland Terminal.
Have a safe flying summer and be careful out there.