A question for ATCOs, 737 input required.

[Capt Claret]

The following situation had me baffled.

Me: 146, about 120 nm NE Alice inbound at F280 for landing with estimate 37. TOPD 69DME (unknown to ATC as they hadn't asked for it)

T'other: 737 (800 I think [VX?]) ex AYQ for Cairns via overhead ASP at > F300, estimate overhead ASP about 37 (see next para).

ATC requested our desired level passing (on descent) at time 27 as a possible requirement for traffic purposes, as they required 10 mins separation, hence I assume 73's est ASP 37.

Given this scenario, and with an inadequate understanding of ATC's requirements, I'm still confused as to why requirements had to be given.

Surely a 737 would be above F300 in 179 nm AYQ to ASP. At the time of passing I expected to be in the circuit at ASP. For me, and this is not a criticism of ATC - just me trying to understand what was going on, there was no conflict.

Can some one please clarify this for me?

[AirNoServicesAustralia]

Opposite direction requirement is time of passing minus 10 minutes so if you were both estimating AS at time 37 then the appropriate vertical requirement in this case 2000ft (assuming you were Non-RVSM, which I would think you are being a BA146), would have to be achieved by time 27. The 737 would have to be at FL300 by time 27 if you were still maintaining at time 27 (hence the question from the controller). The 737 doesn't have 179 NM to be up but 179NM - 10 mins (assuming 6 NM a minute take off 60NM) equalling 119NM to be maintaining FL300. Likely but not worth assuming that especially around Alice Springs where on the hot days the climb profiles can be pretty poor.

I hope this answers your questions.

[ferris]

The above is correct. Nose to nose is tricky and restrictive in procedural airspace. Sometimes the requirements etc sound stupid, but ATCOs are not allowed to assume. Especially if the ATCO is under check or training;)

And every now and again, you do get a surprise. (eg the 737 has cracked his windshield and is climbing slow and hasn't told you.)

[MoFo]

Just for what its worth the 800 series 737 does not perform like the 300 and 400 series. The best comparison is that it climbs more like the old 727. Sedate, but eventually gets there.
I'm sure the ATCOs have noticed.