I recently flew from Boston to LA, and as the plane passed over the Rockies, I was watching the snow-capped mountains below. Suddenly, another airliner rocketed through my field of vision from the opposite direction. Based on the apparent size of the aircraft, I would estimate the distance at about 1000 feet below us, and 3000 feet to starboard. It crossed a field of view of about 120º (two windows wide) in less than 3 seconds. It wasn’t so close that a crash seemed imminent, but yet it still seemed closer than what the FAA allows. Is this typical? What are the regulations on minimum separation between commercial aircraft?
A quick glance through my reg book only yielded “not so close as to cause a collision hazard”, but I don’t have the regs specific to the airlines so maybe that’s where it is. Or maybe I just can’t read this morning.
I seem to recall hearing a thousand foot vertical minimum so what you saw (assuming your distances are accurate) was close to the legal minimum. Instrument flight plan “traffic lanes” are at thousand-foot vertical intervals (eastbound at odd thousands - 9000, 11000, etc. - westbound at even thousands), so if you were going in opposite directions that would be about right.
The horizontal minimum only kicks in if you’re at the same altitude, and if I recall correctly thats about 2000 or 3000 feet - so it looks like air traffic control might have been using both minimums at the same time.
What is too close? Touching, of course.
Sorry - gosh, I’m spacey this afternoon - forgot to add (for the benefit of potential nit-pickers) that I am confining this answer to the discussion of airliners flying in (presumably) Class A airspace. Minimums for other types of aircraft under other conditions may be and are different.
If you were at cruise BOS-LAX you were probably over 29000 feet (FL 290). Separation at those levels is five miles horizontal and 2000 vertical. To make things easy, as Broomstick indicated, nice round numbers are used: FLs 410, 370, 330 and such for eastbound, with FLs 390, 350, and 310 for westbound.
You probably saw an aircraft on a similar J-airway at 2000 feet distance. I watch planes depart Linbergh from my brother’s house at three miles and they look big. 2000 feet apart in the air will look positively intimate.
Does anybody know how close two commercial airliners have ever gotten without colliding? I would suppose in all these years there must have been some rather narrow misses on the order of tens of feet.
At altitude or close to the ground? Not to be facetious, but more often than not, collisions between planes occur at airports rather than at altitude.
IFR veritcal separation is 1000 feet up to and including FL 290. Above FL290 is 2000 feet, with a few exceptions.
IFR horizontal separation depends on quite a few things such as type of radar used, distance from the antenna, whether the aircraft are converging/diverging, wake turbulence concerns, etc. Very roughly, 3 miles if the targets are within 40 miles from the radar antenna, or 5 miles if greater than 40 miles from the antenna.
To pass that close in midair, one wonders if if ‘wake vortex’ would come into effect. I seem to remember a recent incident that downed a plane that took off too soon behind another, and was tossed around by the wake of the first jet. I would imagine the same vortex occurs at higher altitudes as well.
Wake turbulence is more severe when the aircraft is heavy, clean (flaps/lift devices stowed), and slow. For most aircraft, this is the takeoff configuration.
ATC guidelines require increased separation where the effects of wake turbulence is a concern. I could quote it all out of my required text for ATC class, but it doesn’t make for fun reading.
“… altitude difference was 10 meters; lateral distance none.” That was between a 747 and DC-10 (at 36000ft), so that’s about one fuselage diameter. I don’t know if that’s the closest, but it’s pretty close.
Airline pilot here …
As folks have said, above 29,000 feet (ie typical airliner cruise), vertical separation is 2000 feet. At all lower altitudes it’s 1000 feet. The various horizontal separations mentioned are only relevant for aircraft at the same altitude.
It is 100% normal to have aircraft pass directly over or under you by the 2000’ separation with zero horizontal offset. It happens every few minutes on densely traveled routes. You can’t see them out your side windows, but we see them coming right at us all day long.
The advent of GPS has greatly improved navigational accuracy, which has some safety benefits, especially near the ground. But a paradoxical result is that every airplane fololwing a given route is on the exact same track. So somebody coming the other way will pass directly above/below. 10 years ago with less accurate navigation, being within a couple of miles left or right of the desired track was as close as it got enroute, so you often had lateral as well as vertical separation from opposing traffic. Not anymore.
As well, with the ever increasing traffic levels, the 2,000 foot spearation above 29,000 is being reduced to 1000 feet. They’ve been doing it over the North Atlantic for about 6 years now, and in Europe for the last 3 or so. It’ll start changining here in the US very soon.
Seeing another jet aimed right at your nose and getting bigger at 1000+ mph when you intend to pass less than 1/4 mi apart is unnerving at first. We get very good at judging vertical closure angles to ensure he’s really going above or beow, in addition to all the computers on both airplanes and on the ground that are watching the situation.
Somebody asked about wake turbulence. That’s not much of a factor for aircraft at different altitudes. The wake does sink after being created, but by the time it’s dropped 1000 or 2000 feet it’s diffused enough that it’s just one more bump in the sky.
But for airplanes at the same altitude it can be a factor. Many times I’ve gotten a pretty good jolt from crossing behind somebody’s path. The good news is that unless our courses are nearly parallel, we’ll cut acroos the wake in just a couple of seconds tops, so there’s not much time for it to upset our path (or our coffee).
Finally, I don’t know about the winner in the closest near miss contest, but I once flew with an old Captain who had a close call back in the middle 1960s. He was the First Officer that day and they crossed paths very very close co-altitude in cruise with another airline’s 727.
He said when they passed through the 727’s wake a few milliseconds after the impact didn’t happen, their coffee cups bounced off the ceiling.
After a suitable hushed silence ATC asked them if they saw anything, and the Captain said on the radio “Well, the other Captain’s wearing a red baseball cap.” :eek:
I meant closest separation in flight. Both of the inflight stories cited are impressive indeed. 10 meters is about what I would have guessed for the winner, my guess is that any closer calls than that simply can’t be measured with any accuracy.
LSL Guy, that is really interesting information. Last month I flew for the first time in 31 years. I guess I’m over my phobia now and enjoyed the trip. But this is what frightened the heck out of me for so long:
Around December 20, 1972 (close to that date), I was on a flight from Washington D.C. to JFK. I don’t remember how far into the flight we were, but I think perhaps the flight attendants were serving coffee. Suddenly the plane shook like it was going to fall apart.
I was a fairly inexperienced flier and thought that what we were experiencing might be normal. But stuff was flying everywhere and the attendants were holding on and looking at each other with dead serious expressions.
After a few seconds, the plane stopped shaking and the pilot apologized. He said that we had gone through the “exhaust” (as best I remember) from another plane that was 3 miles ahead of us.
I did overhear an exchange between attendants. One said, “I’ve never seen one that close.” The other said, “The FAA will hear about this one.”
Many years later I heard that it was the wake from another plane that took one airliner down near Pittsburg.