Question for the pilots

[Undertoad]

I don't remember what my flight instructor said she'd do if faced with a head-on collision situation. I think she said she'd dive. Or climb. Yeah, I can't remember.

But it seems to me that the BEST approach would be to dive AND turn right. Now, I only had one lesson, so I'm speaking out of complete ignorance here. But I have reasons!

If you only move in one dimension, it seems to me that you would have a greater chance of colliding than if you move in two dimensions. If the other pilot has always thought "I'm gonna dive", and you've always thought "I'm gonna dive", you'd both be planning for your disaster. But if you thought in two dimensions you're improving the chances that your instinctive choice doesn't, er, impact with the other pilot's instinctive choice.

Then, if you turn to the right, you're kinda working with the instincts of autombile drivers, at least in those countries that drive on the right.

Then, if you dive and turn right, you should see the other pilot for a longer period of time and have a greater chance to react.

Is this something you ever consider?

[datalas]

From the way that the news was babbling on, I got the impression that the diving was something to do with the Flight Control System on the aircraft rather than direct pilot action.

Not sure if this is accurate, but thats what was suggested anyhow

[Scred]

on the ground, at 225 mph, race car drivers will tell you that rather than going left or right, you should head right *for* the crash, as there isn't a chance in hell that any of the pieces will still be there by the time you arrive. trying to avoid the pieces only increases the odds of hitting them.

if you know the other pilot is going to try to avoid it, then heading right for him seems the best strategy.

but then again, maybe not. i doubt that your copilot is going to buy into my theory when the time comes.

[Tobiasly]

Undertoad, I don't think your reasoning has as much to do with the number of dimensions as it does the fact that up and down are absolute, while left and right are relative. If both pilots thought, "I'd dive and turn north", they'd be screwed too.

Sure, more dimensions means more combinations, but deciding <i>not</i> to turn right or left <i>is</i> a decision. For each dimension (side-to-side and up-and down -- you don't really have a decision whether to keep going forward ), if you count 1) going one way, 2) going the other way, and 3) doing nothing, then doing nothing has just as good a chance for survival as the other two. (Statistically speaking... of course this ignores the human behavior aspect).

Originally posted by Scred
if you know the other pilot is going to try to avoid it, then heading right for him seems the best strategy.

but then again, maybe not. i doubt that your copilot is going to buy into my theory when the time comes.

And then the other pilot knows that *you* are going to avoid it and heads straight for you...

[Scred]

Originally posted by dhamsaic


And then the other pilot knows that *you* are going to avoid it and heads straight for you...

of course, that *other* copilot would have to be insane as well. that makes four people insane at the same time. i posit this is less likely than both pilots diving and going north at the same time...

[MaggieL]

The official rules are:

When two aircraft are converging, the one "on the right" has the right of way. "On the right" is from the point of view of an observer in the narrower angle betyween the two flight paths. This is why airplanes have red lighs on the left wing and green on the right; if you see a red nav light the other craft has the right of way. Of course, it's smart for *both* craft to simply maneuver to avoid each other.

In the event of a head-on convergence, where both angles are equal, both aircraft are supposed to "break right": turn to their own right. This has the additional advantage of increasing the visual size of your aircraft to the other pilot: an airplane pointed at you is hard to see, but when banked into a turn the wings become much more visible.

These rules are actually based on the "rules of the road" for ships at sea. (Yes, I know there' s no road at sea, but that's what they're called.) Other rules borrowed from terrestrial navigation relate to the priority of various types of craft pover each other, such as sailplanes over powered craft, and airships over heavier-than-air craft. An aircraft in the process of landing has priority over all others.

The reason pilots will dive when in trouble is that they can almost always dive faster than they can climb. Birds know this too. Unfortunately "down" is the same direction for both airplanes, even if one of them is inverted. The pilot usually still knows which way down is.

That's one reason collision avoidance is based on lateral turns. You can reduce the closure rate and accomplish separation faster by *turning* than by any other means....especially if you can avoid turning in the same direction.

This all asusmes you *see* the other aircraft...not always possible. Sometimes one or both aircraft are in cloud, or view is obstructed by the aircraft itself...a high-wing and a low-wing plane in the oattern at the same time with the low wing above is a classic scenario. We do our best to avoid this with careful use of the radio and also Air Traffic Control when available.

In the case in point, there was only one ATC guy working and the conflict alert computer was being repaired.

A new collision avoidance system under development called ADS -B involves having aircraft continually broadcast their high-precision position, direction and speed digitally, allowing in-cockpit display of local traffic and on-board conflict alerting without involving anybody on the ground at all.

http://www.ads-b.com/

[Undertoad]

Interesting. Will they require it of all general aviation at some point? Is it cheap?

[MaggieL]

Originally posted by Undertoad
Interesting. Will they require it of all general aviation at some point? Is it cheap?

Nothing in aviation is cheap...you have to pay the lawyer tax. Anything that is used in aviation runs the risk of a product liability suit filed by survivors of someone who is injured or killed in an airplane. An ordinary screw or bolt costs many times what it would otherwise if it's to be used in an airplane.

That said, there's no engineering reason why ADB-B in particiular any more expensive than any other item of avionics. Because it needs state vector information (position, speed, heading) an ADS-B transceiver is likely to be added as an accessory into a navigation suite that already contains a GPS receiver and a moving map display....so assuming you have the core of a modern nav system design available, adding ADS-B capabilty should not be a big deal: add a transceiver and MODEM to send and receive the data packets, and program the computer[s] to display the targets, and do the tracking and conflict alert functions.

It's the dickens to make *any* avionics a general requirement, considering some aircraft don't even have an electrical system. What's more likely is that operational restrictions will be placed on aircraft not so equipped, once the system gains final approval and there are Technical Standards Orders (TSOs) governing systems designed, performance and certaification.

For example, today an aircraft without a radio must call an airport with a control tower ahead of time by telephone for permission to land. When they show up they''ll be given landing instructions with a light gun (which they do still keep around in the tower in case an aircraft has a radio failure). As a practical matter, it's simpler to just bring a handheld self-contained avation radio along in the cockpit
under most circumstances.. To save the money it takes to get a certification, many GA pilots use GPS systems that are hand-held as well. To get the certifications needed to legally add a bit of electronics to an airplane cockpit with legal assurance that it won't interefere with anything else on board is quite costly.

[MaggieL]

More on the crash...
http://story.news.yahoo.com/news?tmp...iner_crash_152

Apparently the russian pilot has a TCAS alert that told him to climb. TCAS (Transponder Collision Alert System) is a simple-minded cousin to ADS-B; it's a simple reciever that listens to transponder replies in the neighborhood and compares the reported altitude to the current altitude. If it hears a reply that reports something too close to the current altitude, it assumes that the other airplane is a threat; if it was at a very different altitude it's not a factor, and if it's too far away to hear it's not at factor (yet) either.

So...the TCAS aboard the airliner was apparently telling the pilot to climb to avoid the cargo jet, and seconds later the ground controller called on the radio and instructed the same pilot to *descend*. According to the article, the TCAS information is deemed more accurate, and policy is that it to be immediately followed, even in the event of a conflict with ground instructions (while informing the ground controller as soon as possible).

In another touch of irony, German ATC as trying to reach the Swiss controler to tell him *their* conflict alert was flagging the two planes as converging, but the only telephone line to the Swiss controler was apparently busy.

The accident investigation reports on this one will be interesting.

[Undertoad]

When you say that a plane can land without a radio, but has to call ahead of time... does that apply to big airports as well? Can I call PHL up and tell them I'm going to be putting my ultralight down on their busiest landing runway at 6 PM ?

[BrianR]

It don't work like that. You don't take an ultralight into class C airspace and put it where you want to.

The rule is mostly targeted at vintage aircraft such as WW I airplanes. Many old airplanes have no radios or transponders. They are legal to fly but there are restrictions on them. Maggie, you have a more recent copy of the FARs. Can you provide the correct information here?

Brian

[MaggieL]

Originally posted by Undertoad
When you say that a plane can land without a radio, but has to call ahead of time... does that apply to big airports as well? Can I call PHL up and tell them I'm going to be putting my ultralight down on their busiest landing runway at 6 PM ?

The rule applies to airports with control towers, in Class C airspace....like say Reading. Philly International has it's own Class B airspace, which is more tightly regulated. If you wanna be in the Class B without a radio, much less operate out of KPHL itself, you'll need a Very Good Reason to get permission. And ultralight is a whole other story; they are not certificated aircraft, and I'm not familiar with the rules. I doubt you would get permission to operate an ultralight there, radio or no...and with wake turbulance aloft and prop and jet wash on the ground, personally I think it would be very unsafe to do so.

But I can tell you with certainty that if you wanna take anything smaller than a 727 into KPHL, chances are good they will want you to use the shortest 17/35 runway...which is still *plenty* busy.

Remeber, at a tower-controlled field, you must recieve clearance in order to land legally. The clearance will be for a particular runway, at their option; you can refuse the clearance if as pilot-in-command you beleive it would be unsafe. But you'd better have a Very Very Very good reason for wanting 27R, which is the typical arrivals runway for the big guys (assuming a typical wind out of the west)

And the tower is not *required* to clear you at all.