November 2004 Issue

Unicom: 11/04

Grossing Out
I very much enjoyed the article on weight and balance (“Positioning Pounds,” July 2004). It is my understanding that the poor full-fuel payloads we see in virtually all of our Part 23 single-engine aircraft have to do with the manufacturers’ meeting the rather arbitrary 61 knot Vso requirement.

For instance, the new TBM 700C2 max gross weight was increased by 815 pounds because Socata took advantage of an exception to the 61 knot Vso requirement. It had to provide crashworthy seats able to tolerate 20-G decelerations. The Vso for the 700C2 is 65 knots. Same wing and same engine as other TBMs, yet it gets a tremendous increase in max weights. Also, the FAA grants waivers for typical Part 23 aircraft used in unusual circumstances, such as long ferry flights and in bush operations in Alaska. Cessna 180s, 206s, etc., are legally flown hundreds of pounds overweight in these operations.

Like you, I’m not advocating this be done. It’s illegal, can cost you your license and gives your insurer an excuse to wash its hands of your wreck. However, I would very much appreciate a better understanding of the certification requirements surrounding the determination of max weight limits on Part 23 single- and multi-engine aircraft, and whether such determination is influenced by the Vso (and perhaps, I believe, also a balked landing requirement). This might take some research, but I for one would be very interested in seeing an article on this.

-Steve Wagner
Via e-mail

Good question, Steve, and one we’ll definitely use as the basis for an upcoming article. That said, the gross weight of a specific single-engine airplane depends on more than just the Vso requirement. For example, powerplant cooling and landing gear strength are also considered when setting a maximum gross weight value. With respect to Alaska-based aircraft, FAR 91.323 does allow operations at higher gross weights but only under very specific circumstances. But, by no means is this the only way to fly legally at a higher gross weight: Numerous STCs are available for many different aircraft allowing operation at weights heavier than when certificated. It all depends.


Using Strobes
Recent publications targeting runway incursions raise some questions regarding use of strobe lights on the ground. I was taught that strobes are not turned on until the aircraft is cleared onto an active runway or about to cross the hold short line.

This system, almost universally used by airline, visually distinguishes aircraft that are in, or are about to enter, areas where other aircraft are operating at high speed with correspondingly long stopping distances. Turning strobes on just as the clearance onto an active runway is read back provides a backup visual indication to the tower that the aircraft they are talking to is the one they are looking at.

It is difficult to know, as you taxi around in the dark, whether your strobes are causing a problem for other aircraft or ground personnel. This information might only come to you through a radio call which clutters the airwaves and directs your attention inside the cockpit to flip the strobe switch.

I think there is a bit of a knee jerk reaction at work here. “There is a ground operations problem at airports so we should make everyone more visible.” From the reports I’ve read, confusion and not visibility is the cause of most runway incursion problems. Elimination of the visual distinction between aircraft on different sides of the primary operational boundary, addition of visual distraction on taxiways, and discouraging backup visual confirmation of runway entrance clearance, does not sound like a confusion reduction to me.

Visibility within the combined stopping distance of aircraft at taxi speeds is more than adequate with rotating beacon, nav lights, taxi lights and the shadowing of other ground lights. If someone is paying so little attention that they miss all that, I’m not sure that strobes will help. Building the expectation that all aircraft will be flashing so prominently, and night vision degradation from passing strobes, will decrease awareness of other ground hazards such as people, animals, debris and equipment. It could also lead to overlooking an aircraft that has turned off its strobes as a courtesy.

I think this change in recommended practice will be a step backwards in safety if it becomes standard practice. I intend to continue my present practice until the FAA clearly tells me that it is a violation to do so.

-Roger Long
Via e-mail

We don’t disagree, Roger, and were taught the same. Like you, until someone from the FAA tells us otherwise, we won’t turn on our strobes until taking the active and we’ll turn them off as we clear. And that’s not likely to happen. Advisory Circular AC 120-74A,“Parts 91, 121, 125, And 135 Flightcrew Procedures During Taxi Operations,” dated Sept., 26, 2003, includes the following statement: “Prior to commencing taxi, turn on navigation, position, anti-collision, and logo lights, if available. To signal intent to other pilots, consider turning on the taxi light when the aircraft is moving or intending to move on the ground, and turning it off when stopped, yielding, or as a consideration to other pilots or ground personnel. Strobe lights should not be illuminated during taxi if they will adversely affect the vision of other pilots or ground personnel” (emphasis added).

The good news is that the FAA’s August 2004 report says runway incursions have declined in recent years.


Tanks For The Memories
Paul Bertorelli’s article on running fuel tanks dry (“Dry Tanking,” October 2004) struck a chord. Still, I have never run dry one of the mains feeding the engine, because I’m afraid of sucking all the crud from the bottom of the tank and clogging the fuel line. Is this a legitimate concern?

-Mike Stevens
Via e-mail

If you have crud in your tanks, you’ll see it when you sump them. If you don’t see any, your tanks are probably clean. Still, that’s why our airplanes have fuel system screens—one in the selector and one in the fuel pump, at minimum—to catch all that stuff. If your screens are clean, as well as your sumps, there shouldn’t be anything to worry about. It ever hurts to know where the nearest airport is, though.