Date: 201303
Local time of day: 1801-2400
Location: ZZZ.ARTCC, US
Weather elements / visibility: Turbulence
Aircraft: A320
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Descent
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Second aircraft: PC-12
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: General None Reported / Taken
Contributing factors: Procedure
Primary problem: Procedure

Narrative: While working [two sectors] combined. An A320 asked for a lower altitude because of choppy ride conditions. The A320 was at FL310 which is the lower limit of my stratum in that area. I put an interim altitude of FL310 in the data block; and entered an assigned altitude of FL290 and initiated the hand off to the sector below me. The hand off was accepted and the interim altitude was taken out by the lower controller and I gave the A320 the descent. Shortly after the A320 started their descent and were passing through FL304; the pilot of the A320 advised that 'he had traffic at FL290 right in front of him at his 11 o'clock. I didn't see a limited data block because FL290 was below my altitude limits so I tried to quick look [the lower sector] twice; not realizing they were combined with [another sector]. Just as the A320 showed FL302; The CA started to flash and I saw a PC12 level at FL290 right below the A320. I immediately advised the A320 to maintain FL300 and called [the lower sector] but they were in the middle of a transmission; I then received a call from what I think was the D-Side at [the lower sector] and I advised that I had stopped the A320 at FL300. I never saw the A320 go below FL300 and I do not believe there was a loss of separation; however; if the A320 had been descending faster and/or had not been paying attention to the traffic either through his TCAS or visually this would have been a loss of separation with a very low MOC. The RADAR targets were very close to being right on top of each other. The A320 pilot didn't say he received an RA so I believe he was just watching his TCAS or had visually scene the aircraft. This is my second facility. If there was one thing that bothered me most about the way traffic is worked at [my first Center] it would be the use of what we call the 'flash through' or interim altitude procedure. This procedure in my mind is dangerous and should not be used the way it is used here. Basically; if you have an aircraft that wants higher or lower; the procedure here is to put in higher or lower the data block and flash to the next sector. The next sector then accepts the hand off and takes out the interim or assigns another interim they can accept the traffic at and the transferring controller assigns the aircraft that altitude. To take this one step further; if the aircraft is close to the boundary of another sector; the initial receiving controller can elect to 'flash the aircraft on to the next sector'. There have been plenty of times when I have seen this procedure create confusing situations and also more work for controllers through the resulting coordination. It is extremely easy to create an unsafe situation with this procedure as seen with the above example with the PC12 and the A320. I have tried voicing my concern about this procedure since I started training on the floor and it has taken me a long time to even begin to become comfortable with it. This procedure is so ingrained that it is almost impossible not to participate in it and still work traffic. Obviously; because it is the accepted practice here; it is difficult to voice my concern and have it met with open ears. I think it is a misconstrued use of AIT procedures and I would like to see this procedure stopped or at least used with more restriction.




Synopsis: Enroute Controller described a near separation loss; claiming the facility 'flash through' procedures are dangerous and should be terminated.