Flight Crew Air Transport Pilot (ATP)
Confusion; Human-Machine Interface
Aircraft Equipment Problem Less Severe; Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Undershoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Aircraft; Weather
[We were] cleared to descend via the GEELA 6 RNAV arrival with a Runway 7R transition. Autopilot 1 had been engaged since leaving 500 FT MSL on departure. Wind during the descent was out of the southwest above 7;000-8;000 FT at an average of about 25 KTS. However; the velocity varied both up and down about 10 KTS during the descent. We crossed HYDRR Intersection at 16;000 FT (in the middle of the altitude window) and 270 KIAS (5 KIAS fast). We did slow to 250 KIAS by GEELA although I don't recall the altitude. The autopilot had the aircraft on the pink donut in the descent to 10;000 FT at PUNNT. I was a bit concerned about the speed since we were still indicating 250 KIAS. The PUNNT restriction also has a 230 KIAS speed restriction. I was considering using the speed brakes as I wasn't sure we would make BOTH 10;000 FT and 230 KIAS at PUNNT even though we were on the donut. I thought we might just be at a maximum of 240 KIAS and 10;000 at our current rate; so I felt no need to INTERVENE. However; at 10;500 FT the autopilot pitched the nose up; initiating the slowdown to 230 (I thought it was going to get to 10;000 and then slow down). Hence we crossed PUNNT at 10;500 (500 FT high) and 230 KIAS (on target speed). We had a slight quartering tailwind from the right at the time. In hindsight; there is not enough mileage between HYDRR and PUNNT to lose 6;000 or 7;000 FT AND slow up 35 KIAS. My old descent planning rule of thumb is 3 NM per 1;000 FT of altitude loss plus another 1 NM for every 10 KIAS in speed reduction required. There are 19.7 MN between the two intersections. Subtracting 3.5 NM for the required speed reduction means you only have 16.2NM for descent purposes. It is difficult (and not very efficient) to come down and slow down at the same time. If you cross HYDRR at 15;000 (the bottom of the envelope) you require a descent rate of 308 FT/NM. Crossing at 17;000 (the upper end of the envelope) ups the descent requirement to 432 FT/NM. I believe these are unrealistic numbers; even in calm air. Use the speedbrakes earlier if there is anything (altitude or airspeed) that is starting to stray on this arrival and runway transition. I know from plenty of experience that there are no problems when landing to the west with this RNAV arrival. This arrival should be re-engineered or thrown out.
A319 Captain reports missing the PUNNT crossing restriction on the GEELA 6 arrival to PHX. The FMGC had been properly programed and showed on path until 10;500 FT when the autopilot pitched the nose up to slow to the required 230 KTS and crossed PUNNT at that altitude.