Nuisance TCAS Alerts over Kalaeloa

Pilots operating in or near Kalaeloa airport Class D airspace (aka John Roger Field, PJRF) are aware of the proximity to Honolulu Airport and the complex overlaying Class B airspace. Significantly, the instrument approach path to HNL runway 8L crosses the departure end of JRF runways 4L and 4R. In fact, the final approach fix for the ILS 8L approach coincides with the EWABE locator outer marker, which has the physical appearance of a garden tool shed with a circular fence surrounding it. Regular visitors to Kalaeloa are used to seeing big birds overhead while in the pattern. What most are not aware of are the number of traffic alerts (TA’s) or resolution advisories (RA’s) triggered by the proximity of general aviation aircraft right underneath the approach path, some of which may cause tense moments in the cockpit, and some spill over into the offices of the FSDO. Carrier pilots are required to follow standard operating procedures when a resolution alert is issued. In particular, it is mandatory for aircrews to respond to or comply with resolution advisories (RAs) unless it puts the airplane in a dangerous situation. This is dictated in the Aircrew’s Operational Specifications and the FARs. The reporting of these alerts to ATC or FAA is a move by the aircrew to “respond” or to formally react in some way.

Traffic Alert and Collision Avoidance Systems (TCAS) are a mandated feature of all air carriers. The systems operate off of secondary surveillance radar signals and are thus independent from ground-based facilities to give crews an early heads-up on potential traffic conflicts. Because the systems receive and interpret transponder returns from other aircraft they are also prone to altimetry errors or can be caused by misleading mode C signals – one of the reasons to have the pitot-static systems and transponder checked and certified regularly. Airborne Collision Avoidance Systems operate under highly sophisticated algorithms that take into account the operational altitude, speed, and direction of a perceived ‘intruder’, and the climb or descent rate of the target. For an exhaustive and technical explanation, you may want to consider reading the ICAO ACAS manual. Another good source of this information is the Advanced Avionics Handbook (FAA-H-8083-6, page 5-14).

Separation levels between aircraft operating under instrument flight rules (IFR) and those under visual flight rules (VFR) are 500 ft. TCAS systems will issue resolution alerts when separation is less than 400 ft (above 1000 ft altitude). A closer look at the Honolulu ILS Rwy 8L descent profile and the protective Class B airspace reveals that an aircraft flying the electronic banister will be at an altitude of just under 2000 ft at the final approach fix, EWABE. The locator outer marker (LOM) also happens to demarcate the step-down border between Class B floors from 1900 to 1600 ft.JRF TCAS

Let’s consider the following scenario: A pilot is leaving the Kalaeloa pattern north-west bound shooting touch-and go’s on runway 4R. The tower controller advises to extend the upwind leg before turning on crosswind because of traffic in the pattern of the parallel runway. The pilot begins a climb after leaving the pattern , reaching an altitude of 1899 ft just inside the 1900 ft floor of the Class ‘B’ altitude (take note: the floor of Class B includes 1900 ft!). At this time, an air carrier is crossing the FAF at EWABE. In this scenario, vertical separation could be as little as 100 ft (see figure) without any overt airspace violations! Of course, this flight profile makes no practical sense. More realistically, a pilot might want to climb to 1500 ft and turn towards the Waipahu Sugar Mill reporting point early to pick up a clearance to HNL. This pilot may find herself under the 1600 ft Class B floor and and 300 ft below an aircraft on the ILS. The possibly ensuing turbulence in the GA aircraft cockpit may not be as bad as in the first scenario but may trigger a similar ‘close call’.

Nuisance alerts are still alerts – the nuisance aspect comes in after-the-fact. At minimum, they distract the flight crew from more important tasks three minutes before touch-down. At the other end of the spectrum is an inquiry from the FSDO. Evidently, Honolulu has seen recent spikes in such close calls.

The area between Kapolei and the H1/H2 interchange has arguably among the highest traffic volume on Oahu, both in the air and on the roads. Consider the following facts. VFR traffic leaving HNL will likely be at 1500 ft near the interchange and may continue westbound (training aircraft destined for the practice area and aircraft inbound for JRF). Traffic inbound for HNL will be at or above 2000 ft, turning towards Ford Island once cleared into Class Bravo. Traffic inbound to JRF is kept at or below 1500 ft and is cleared into class D from the “quarry”, just north of H1 freeway. These aircraft will descend to pattern altitude on the 45 degree entry to the left downwind for runways 4. Aircraft departing JRF will initially turn towards the quarry at pattern altitude, before turning north-east. It is prudent to maintain pattern altitude while approaching or leaving the JRF pattern. By the same token, consider inbound traffic from the quarry, descending out of 1500 ft, and any transitioning traffic near the H1 freeway.

Pilots may also not be aware of an agreement between Honolulu and Kalaeloa concerning the control of Class D airspace 1500 ft or more above PJRF. While formally under the control of Kalaeloa Tower, Class D airspace above 1500 ft is managed by Honolulu ATC. If you ever ask for a clearance to transit through Kalaeloa airspace above 1500 ft  you will be advised to contact HCF approach on 119.1 Mhz.

Disclaimer: The opinions expressed in this post are subjective and the information, while thoroughly researched may be incomplete and time-sensitive. Always consult official aviation publications.



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