B737-700
Air Traffic Control Fully Certified
Human-Machine Interface; Confusion; Communication Breakdown; Distraction
ATC Issue All Types; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Chart Or Publication; Human Factors; Procedure
I was working a couple of jet arrivals on the KOOLY RNAV STAR to PHX with a B190 on the SUNSS arrival. We give the turboprop arrivals 110 at the boundary. When we have a jet overrunning the prop; we give them either 120 on the short side or 140 on the long side (downwind leg); per the LOA; and coordinate that they aren't descending via. The problem with this lies with the phraseology. In the past; we would give them a descend via clearance [along] with the [planned runway] transition; with an 'except clearance' to cross SQUEZ at and maintain either 120 or 140. The pilots would read it back; but miss the maintain part. In other words; they wouldn't stay at 120 or 140; they would cross SQUEZ at that altitude; then continue to descend via. We then got into the habit of saying cross SQUEZ at and maintain 140 (or 120); then fly the 7R (or 25L) transition; but do not descend via. It was wordy and clunky; but worked for the most part. I then got into the habit of clearing them early enough for the transition; with an intermediate altitude to maintain (which accomplishes the same requirement to give the transition without the verbiage). In this case; I gave a B737 the transition and a clearance to FL190 ('...you're cleared via the 25L transition; for now descend and maintain FL190). Subsequently; I gave them a clearance to cross SQUEZ at 120; which the pilot acknowledged. I had shipped the prior jet (who had had trouble with the clearance; thinking I was giving them descend via) to PHX; when I noted the 737 had about 110 KTS on them. I reduced the 737 to 250 KTS and told them to resume the rest of the speeds after SQUEZ. I asked them what their speed was; they said 310 KTS (around KOOLY where they were supposed to be doing 280 reducing to 270). They thought I was giving them descend via again; so they asked if I wanted them to descend via. They then said they would be high at SQUEZ; so I turned them out to the left (plus I wasn't going to keep the spacing with the Beechcraft). They told me that I gave them a late speed reduction and I told them the speeds on the RNAV arrival were mandatory unless otherwise cleared (which they assured me they did not receive). They then came back with a remark of the nature of 'you want us to descend via now since you want the speeds.' Had I not noticed the speed or turned the B737 out; I probably would have had a deal.I had a discussion with the national RNAV workgroup in which another pilot said that they don't fly the speeds unless given descend via. Since we cannot always give descend via but need the speeds for spacing; it puts us at a huge expectancy issue. I found this reference in the AIM (5-4-1a1) that I think should be distributed as a bulletin to all of the airlines and GA groups (as well as GAMA): 'STAR/RNAV STAR/FMSP procedures may have mandatory speeds and/or crossing altitudes published. [...] Published speed restrictions are independent of altitude restrictions and are mandatory unless modified by ATC. Pilots should plan to cross waypoints with a published speed restriction; at the published speed; and should not exceed this speed past the associated waypoint unless authorized by ATC or a published note to do so.'
Confusion reigned when ATC--in an effort to maintain separation between a BE-190 on the SUNNS STAR to PHX and a B737 on the KOOLY RNAV STAR (both of which STARs include waypoint SQUEZ)--mixed 'descend via' phraseology with altitude assignments different from those on the STAR charts themselves.