Date: 201701
Local time of day: 1201-1800
Location: ZHU.ARTCC, TX
Light: Daylight
Aircraft: Medium Transport
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Descent
Airspace: Class A ZHU
ATC / advisory: Center ZHU
Second aircraft: Medium Transport
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness; Confusion; Distraction
Second reporter function: Enroute; Handoff / Assist
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Contributing factors: Weather; Human Factors; ATC Equipment / Nav Facility / Buildings
Primary problem: Human Factors

Narrative: There was weather in the sector. The Northeast corner post of Houston Approach was shut off; and all arrivals from the east were coming through my sector. Halfway through a very busy arrival push; the Supervisor instructed me to send six aircraft to another corner post and for me to hold the remaining aircraft I had on frequency. This was all due to weather. I Instructed Aircraft Y to proceed direct GIRLY intersection to hold at FL200. I also instructed Aircraft X to proceed direct GIRLY intersection and to hold at FL220. On the way to GIRLY intersection; Aircraft X advised that they will not be able to hold and requested clearance to Lake Charles Regional Airport. I cleared Aircraft X direct Lake Charles Regional Airport and issued a descent clearance to 150 due to traffic at 140. The pilot of Aircraft X requested a vector of 020 due to weather; which I issued to the pilot. When Aircraft X was at FL217 descending to 150; I instructed the pilot to amend their altitude to maintain FL210. The pilot of Aircraft X stated they were unable to maintain FL210. I then instructed Aircraft X to stop descent and climb to and maintain FL210. Separation was lost between Aircraft X and Aircraft Y.


Second narrative: Aircraft Y entered the hold and on the way to GIRLY Aircraft X decided to divert to LCH. As the D side I placed a 'halo' around Aircraft X to remind the R side to check the area since we had other aircraft in the vicinity. As the R side was giving the clearance to Aircraft X I was on the land line with approach Approval Requesting an EFD lander off route. I did not hear the R side assign an altitude or a vector (requested by the aircraft because of weather) to Aircraft X but when I got off of the line I heard him tell Aircraft X to amend altitude and maintain FL210 (MODE C on the data block indicated FL217 at the time of the clearance). The pilot of Aircraft X said 'unable' and the R side advised him to return to FL210 but separation was lost between Aircraft Y in the hold at FL200 and Aircraft X descending. I believe that this event was a direct outcome of the R side working so much on the sequence and weather and then holding clearances and when it slowed down a mistake was made.I don't have any specific recommendations. I believe it was an honest mistake that took place because the R side had just had a very stressful session and when it calmed down this happened. I do not feel the R side was negligent or unprofessional at all; I think it was an oversight and a onetime event for the R side.


Synopsis: ZHU Controllers reported of a separation loss when the RADAR Controller requested an aircraft to stop its descent; but the pilot reported they could not.