Separation at Altitude for the lay-person
 

Following on from my recent in flight experience here:

http://www.pprune.org/australia-new-...oke-cabin.html

I was a passenger early this morning on a 737-800 at cruising altitude (39,000 feet?), just south east of Roma according to the inflight map.

I was filling out the passenger arrival card when I noticed a flash across the seat back in front and turned toward the back of the plane to see another aircraft at the 4 o'clock position and heading at a 45 degree angle away to the south and at near enough the same altitude.

I wish I had taken a photo but it was definitely a jet aircraft with an unpainted/silver underside.

To me it 'appeared' that the other aircraft was very close and, thinking about it, would have been closer moments before I saw it.

Am I a paranoid passenger? Is this kind of thing normal?

Was in any lower/higher than 330m?

Remember they look big….even at much further away than that.

Probably quite OK.

Fairly certain that you would have noticed evasive action from the Traffic Collision Avoidance System (TCAS) alert.
It would have been ok.
I have had a 737 pass 1000ft above me and it looked massive and super close.

1000ft vertically (330m) is the norm and it does look close. even as a pilot with 20,000hrs I enjoy watching other aircraft pass, and we have minutes warning of the impending passing. seeing one without warning out of a passenger window can be disconcerting if your a slightly nervous flyer.

I did my ATC training in the days before TCAS. We were taught if two aircraft were going to pass directly over each other in the cruise then advise the pilots, because even from the front seats it was hard to visually judge vertical separation.

Another aircraft 2 miles away and 1000 feet below is only 5 degrees below horizontal (assuming I've done the maths correctly).

It's even more impressive watching aircraft above and below you in a holding pattetn at altitude.

About 20 years ago had two memorable experiences.

1st was given a clearance to transit Avalon coastal in an archer at (I think - might have been 2500) and given traffic as a 747 doing circuits at 1500'. Passing the upwind end of the runway, had the 74 climbing directly towards me - awesome sight as it turned away for crosswind seemingly only a mile or so away.

2nd was in the same aircraft, Moorabbin to Echucha in a howling northerly at 6000'. Traffic advised as a 747 1000' below right to left. Sure enough a united 747 on base for Tulla passed directly underneath with what looked like a 20 degree crab.

Doesn't seem to happen so much any more.

UTR

Nowadays you'd probably have to divert 20nm before resuming own navigation for traffic separation.! :}

I've seen an RFDS PC-12 pass from left to right underneath a QF 737 I've been on (as a passenger) on the way into Adelaide.

Must have been at least 2000-3000 feet below, but even a PC-12 can look relatively large at that distance.

Well, I've had it the other way round. Been IN a RFDS PC12 and watched a F100 jet go past 1000' below in the opposite direction. It looks pretty big and the closing speed is even more impressive... :E

To the OP, I would think that what you saw was probably all above board. It is just that if you happen to snag a direct under/over pass with another aircraft at minimum separation height it looks pretty scary close if you weren't expecting it!

5000FT vertical seperation to A380
 

That machine is huge, when I went under the flight path of the initial A380 YSCB to YSSY from west to east at 5500FT some years ago.

Called departure from CB as FL110 for SY and via CULLERIN, after a circuit on the Telstra tower!!

It is a certain spacial reality check. While 1000 feet may seem quite a bit, vectoring it out the line of site, (especially without ref at 39K feet), it may seem about level.

An Aircraft such as a 747, is 250 feet long, so the 1000 feet is only 4 aircraft lengths in spacial reference. That will appear very close whn looking out the windows.

Now, if you can see a shocked look on the drivers face, :eek: then I would be concerned.

When light and high (reduced ambient aerodynamic noise) you can occasionally hear the whoosh of opposite direction A330/777, 1000 feet above

It was once not uncommon for the US Starlifters and Galaxies YSRI-YBAS to have their clearances denied by SY DEPs (usually due to a u/s or temperamental txpdr), resulting in them flying out to PKS OCTA. Was interesting viewing a 1200 paint with a g/s of about 90kts op direction to a C5 500' above. Would have been intimidating in the 150 or whatever it was, I'd imagine it would be something akin to a shadow falling over the sun!

Once flying into YMMB in single from YNAR in CTA, we were vectored over Tulla' at 6000' then out over the bay descending to 4000'. A Cathay Pacific 747-400 was departing to the south. My rear seat RHS pax called it out to me that he was there. We watched as it climbed closer to our alt on a similar heading, only about 2-3nm away. At about 500' or less below us, ATC gave the CX747 an immediate right turn and me an immediate left, then asked me if I wanted to submit a report on the breakdown of separation. I replied that we had the 747 in sight the whole time and enjoyed the close up view of it in flight, to which the ATC guy seemed relieved.

I doubt he would be relieved, except of his position, as I expect Cathay pilots would submit incident report - rightly so.

Immediately Reportable Matter?

I'm just guessing but
suggests it was in the good/bad (delete as appropriate) old days. It would be professional suicide to ask something like that today.

May well have been me. Will certainly never forget it. Centre "warned" me of the crossing traffic but if I remember correctly it was only 1000' as I'd stopped climb at FL180 and it was descending to and had just reached FL190. Let's just say that if I had not had the heads up from ATC I may have needed a change of
underwear!

Maintained 5000' on a 34 DOSEL SID out of Melbourne recently with inbound traffic at 6000' positioning on the ARBEY for 27. Us in the right turn, them in the left turning downwind. 1000' vertically separated but essentially pointing our wing tips at each other. Looked freaking awesome but I'm surprised that one of the pax didn't call the media to claim a near miss.

The other one I've done a while back was established on 16L into Sydney when a 744 was vectored onto 16R a couple of hundred feet above or below. We got a great view of their underbelly as they rolled onto final. It was so impressive (and potentially newsworthy for someone who had taken a photo) that I made a PA on the ground explaining what had occurred and our differing altitudes, etc.