Unicom

June 2005 Issue




Unicom: 06/05

I was dismayed to read yet another rendition of the downwind turn myth in “Learning Experiences” (April 2005). Gripped by the fate of an ice-laden, 1960 Travelair, I almost missed “...I wanted [to] do a 180-degree turn, but the winds were strong and increasing in velocity; I feared a stall. Groundspeed dropped to under 80 knots...”

Thank goodness the headwinds didn’t pick up another 15 knots and cause the unfortunate aircraft to fall from the sky because of insufficient groundspeed. He was lucky to have had the horsepower to avoid the fate of all the other planes that fell out of the sky that day.

Wouldn’t it be appropriate for a safety magazine to comment on the breach of aeronautical knowledge in this piece? What was the “lesson learned?” Sadly, this article reminded me of your disservice to the community several years ago, when you published Richard Collins’ downwind turn hogwash.

Andrew Swart
Via e-mail

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And Losing Vacuum Pumps
In the first of two “Learning Experiences” published in April’s issue, is the writer reverting to the downwind turn myth in writing “I feared a stall” when discussing wind and groundspeed?

In the second, losing both vacuum (or pressure pumps) does not happen often but is reason to be current on needle-ball-airspeed aviating!

Charles Nicholson
Via e-mail


We typically don’t comment on Learning Experience submissions; we do, of course, edit them for length and style. In this instance, we left in the reference to the pilot’s fear of a downwind turn close to the ground more for dramatic effect than anything else. To us, his reference to a loss of groundspeed underscored the adverse conditions with which he was dealing, irrespective of the aerodynamics.

And, yes, being sharp on partial panel is the best defense against losing your gyros, but keeping tabs on the state of your vacuum/pressure system and any backups is also a good idea.

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A Sober Look At Cirrus
Good article on the Cirrus (April 2005)! Cirrus shares a common link with legacy aircraft being outfitted with glass cockpits: pilots are often spending more time with the PFD/MFD and associated electronic controls at the expense of flying the airplane. Many a techno-savvy pilot likes to perform multiple cross checks with the electrons, or explore electronic capabilities, and is focused on those electrons. Many a non-techno-savvy pilot trims the airplane and enters the “ground school zone” at 110 knots.

The glass cockpit in any airplane is a matter of human factors, aeronautical decision making and flight condition perceptual awareness. Is the pilot managing the glass as he/she flies, or is the glass mesmerizing the along-for-the-ride pilot? No manufacturer can design a “safe” airplane for the pilot who is along for the ride.

Gregg Monaco
Via e-mail

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Purkinje Shift?
In “Bumps In The Night” (March 2005), Adrian Eichhorn discussed the physiological effects of darkness and night flying. Besides autokinesis, Adrian mentions Purkinje Shift (certain colors are perceived differently). I’ve done a little fishing—excuse me—research and can’t find a good physiological description of this term. Can you or Adrian elaborate?

Dudley Wireman
Via e-mail


“Purkinje Shift” describes the effect of light on colors perception by the human eye. In low-light conditions, the rod receptors in the eye take over from the cone receptors, both of which are most sensitive to different wavelengths of light. As it gets darker, we perceive colors as changing in brightness—reds and oranges grow relatively dimmer and greens and blues grow relatively brighter.

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DUAT Session Length
At the end of your excellent article, “Incomplete Briefing” (March 2005), you stated that the pilot did not spend enough time online during a DUAT session to understand the weather picture. Maybe so. But my flight planning software (Destination Direct) downloads my briefing and immediately signs off. I can then peruse the information as long as I wish without tying up the line. So the length of the DUAT session does not necessarily indicate how carefully the pilot examined the data.

Daryl Biser
Via e-mail


You’re right of course—many flight planning software packages include this feature. But it appears from the NTSB’s report on this accident that the pilot was not using this level of automation for his planning and, instead, conducted an interactive session.

The NTSB report states, “The pilot listed himself as pilot, checked NOTAMS, and terminated the DUATS briefing at 12:39:53. The pilot [then logged on a second time, filed another flight plan], checked NOTAMS and terminated the DUATS briefing at 12:41:24. No en route weather information was requested during the DUAT sessions.”

Based on this information and the pre-flight weather information that was available, we concluded a full briefing would have alerted him to the possibility of severe turbulence along his planned route.

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Inadvertent Night IMC
Thank you for the recent article, “Bumps In The Night,” regarding the additional risks associated with night flying (March 2005). The subject is one I have been mulling over for several weeks in light of a recent experience that has caused me to modify my personal minimums.

On a recent night flight, I had filed IFR because of some marginal VFR weather. I would most likely not have filed IFR for a daytime flight.

About 30 minutes into the flight, I was surprised to discover that I had entered solid IMC without expecting it. The only way I knew I was in the clag was that my strobe lights began to reflect and I had to shut them off. Additionally, the wings and windshield began to ice up almost immediately. We went from VMC to IMC with ice without any clues or warning.

When I was not Instrument-rated, I had a similar experience in a Cessna 150 Aerobat—less the ice—and managed to climb out above the layer.

My personal minimums have changed as a result of these two experiences. I simply will not fly at night without being on an IFR flight plan. Period.

My advice to VFR pilots is to avoid night flying unless the forecast is for perfect VFR and there is some sort of moonlight with which to spot IMC before it’s too late.

I would be interested to find out how often Instrument-rated pilots have had similar experiences. I would not be surprised to find it has happened to nearly everyone.

Thanks for the great publication.

Al Browne
Via e-mail

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The 70 Percent Rule
In light of what was revealed in your excellent article, “Your POH Is Lying” (May 2005), the “70 percent” rule could be an excellent backup safety measure. This rule is based on continous acceleration from brake release to Vx—no matter the runway length or density altitude, if you don’t have 70 percent of Vx at the runway’s mid-point, your airplane is accelerating too slowly.

This rule has been promoted by Bill Kershner since the 1950s. Two fatal accidents to which I’ve been close in the past three years could have been prevented by the 70 percent rule and four people would not have died.

Bill Lee
Via e-mail