Denver Center (ZDV) will utilize capping and tunneling procedures during significant WX events or when high or ultra-high altitude sector volume is such that an operational advantage can be gained by utilizing the low altitude stratums in and out of the Denver terminal area.
Procedures Description:
For this plan "CAPPING" refers to restricting departure aircraft at a lower altitude until a point in space beyond the constrained area, typically AOB FL260. Beyond that point these capped flights can safely climb to their requested altitude. ZDV TMU utilizes two capping initiatives: Terminal capping and enroute capping.
For this plan "Tunneling" refers to the practice of descending DEN area arrival aircraft sooner than normal and continuing to their destination airport below the constrained area.
Capping Plan Description:
Enroute Capping
During large thunderstorm events rerouted flights may cause volume issues in numerous ZDV high altitude sectors. One mitigation strategy to relieve pressure on these impacted sectors is to cap departures from the Denver Terminal area AOB FL260 Westbound AOB FL250 Eastbound. During a Severe Weather Avoidance Plan (SWAP) event ZDV TMU will work with the Area supervisors to identify and coordinate the need to cap DEN departures.
Since flying longer distances at lower altitudes burns more fuel, coordination with the aircraft operators shall be accomplished via a published advisory through the Command Center. We should also ask the dispatchers to remind the pilots to not ask for higher during these Capping Initiatives. TMU will also need to coordinate with adjacent facilities if the flights will remain capped until a point inside their airspace.
Tunneling Plan Description:
The practice of tunneling aircraft below constrained airspace may occur during periods of heavy enroute volume and/or complexity. During certain scenarios, ZDV will descend DEN area arrival aircraft sooner than normal to continue to their destination airport below a constrained area. This allows ZDV to reduce congestion particularly in high and Ultra-high sectors. Also, in certain scenarios, ZDV may need to tunnel departures from adjacent facilities that are intending to climb into our congested high-altitude airspace--that are also intending to land in the DEN area. At ZDV, tunneling is typically accomplished on a more tactical basis than capping procedures, but if impacts are expected to be more than minimal, ZDV TMU will accomplish necessary coordination with affected facilities and users.
Altitude/Routes/Distance:
The altitudes, routes, and distances for all Capping and Tunneling procedures will need to be determined dynamically for each weather/sector complexity scenario.
Impact on Airspace:
These capping and tunneling procedures may add significant volume and complexity to our low altitude sectors, therefore additional TMIs (i.e. miles-in-trail) may be needed to manage the additional volume in those sectors.
Internal/External Facility Impact:
ZDV impacts will depend on the specific Area and sectors that are experiencing volume and complexity issues due to severe weather reroutes. ZDV sectors are very large, so the point-in-space where Enroute Capping procedures end and departures are allowed to climb higher may be several hundred miles away, possibly extending into adjacent facilities' airspace. Pre-coordination with our neighboring ARTCCs (ZLC, ZKC, ZMP, and ZAB) may be required if this occurs.
Additionally:
In addition to the coordination described above, all plans to cap or tunnel should also be briefed at ZDV stand-up weather briefings, and on all ATCSCC planning telcons.