Date: 201703
Local time of day: 0001-0600
Location: ZMP.ARTCC, MN
Aircraft: Gulfstream V / G500 / G550
Flight plan: IFR
Flight phase: Descent
Airspace: Class A ZDV
ATC / advisory: Center ZDV
Second aircraft: A320
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Communication Breakdown; Confusion; Distraction; Human-Machine Interface; Situational Awareness; Time Pressure
Second reporter function: Enroute
Anomaly: ATC Issue All Types; Airspace Violation All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Separated Traffic
Contributing factors: Human Factors; Procedure
Primary problem: Procedure

Narrative: This is the third one that happened within an hour and twenty minutes of each other. I was in the process of closing my sector for the evening (ARCTIC). My airspace is FL390 and above. As I was starting to hand off aircraft to the sectors below me (WILD; and HAWKI) I noticed that Denver 9 was handing off Aircraft X to me level at FL410. Then I noticed that they took the handoff back. I started my briefing to the HAWKI sector they own the airspace on the east side of ARTIC FL380 and below.After finishing my briefing with HAWKI I began my briefing to the WILD sector. They own the west side of ARCTIC when it's closed FL350-FL380. As I was completing my briefing and before I called the adjacent sectors to tell them I was closed I noticed that I just had a limited data block on Aircraft X still level at FL410. Aircraft X was getting very close to our boundary so I asked the WILD sector if they were watching Aircraft X. He asked me if Aircraft X was descending to FL330 and then he hung up. He immediately called the Denver 9 sector and asked them if they were descending Aircraft X to FL330. Just then the conflict alert went off with Aircraft Y at FL360! The Denver Controller asked the WILD Controller if he should stop Aircraft X at FL370. The WILD Controller said affirmative. Our letter of agreement with Denver Center is that they need to get Lincoln landers down to FL330 by our boundary. The Denver Controller violated Sector ARCTIC and WILD by descending Aircraft X through their airspace without a point out or handoff. And they violated our letter of agreement.Denver Center's blatant disregard for separation is astonishing to me. The fact that this has been going on for 20 plus years and nothing has been done about it is just as astonishing! If the WILD sector hadn't noticed that Aircraft X was descending through his airspace there could have been loss of separation or loss of human lives. Management is well aware that Denver Center hands us conflicts on a daily basis and I don't see anything being done about it!


Second narrative: I was the radar controller at Sector 42; and the traffic level was coming down from being a red sector. Arctic (sector 40) was just being closed as the event happened. There were quite a few airplanes on the west side of the sector at FL360 and FL380 in a small area; as I was getting the briefing from sector 40 the controller there noticed an aircraft at FL390 about to cross the ZMP/ZDV boundary with no handoff; point out or Plan View Display (PVD). He mentioned it because it could be an issue; so I pulled the data block up. It was Aircraft X at FL390; and the data block reflected that they were descending to FL330. They were landing LNK. Per the LOA; ZDV must have LNK landing traffic level at FL330 or below. This aircraft crossed the boundary at FL390 descending to FL330 with no point out or Approval Request (APREQ) with ARCTIC or WILD; and sector 39 had the handoff. Once I noticed they were descending I PVDd Aircraft Y at FL360 up to ZDV sector 9 who was working Aircraft X and called them asking if they really were descending to FL330. They didn't have a response but then APREQd Aircraft X stopping at FL370. Aircraft Y and Aircraft X were head on traffic with Aircraft Y level at FL360 and Aircraft X descending out of FL390 for FL330 and only about 20 miles apart. Conflict Alert was going off. Furthermore ZDV sector 8 had the handoff on Aircraft Y; Aircraft X was less than a mile from ZDV 8's airspace. ZDV 8 should have received a point out on Aircraft X and noticed there was traffic (Aircraft Y). So Aircraft X entered sector 40 and 42's airspace without a point out or handoff descending into traffic (Aircraft Y). This is also a violation of the LOA with ZDV and ZMP as they were supposed to be level at FL330 by the common boundary.This happens often as ZDV does not get LNK or OMA landing traffic level at the ZMP/ZDV boundary as stated in the LOA. Their controller needs to adhere to the LOA and get the traffic at the appropriate altitude so these problem won't happen again. This was a very dangerous situation that we continue to see with no changes happening.


Synopsis: ZMP Controllers reported an airspace violation and two aircraft head on at high altitude; caused by ZDV Center.