Page 10 - April21T

Near-Hit
Teachings from a reader’s
Aclose call with a midair collision. by Thomas P. Turner
Twin & Turbine reader recently wrote about a U.S. Part 91, while Part 135 requires it in airplanes with harrowing experience: 10 or more seats. The MU-2 does not meet any of the
I was almost involved in a midair a few weeks ago. I fly an MU-2 and was in IMC on an IFR
my home airport, Hazelton Regional (KHZL) in Pennsyl- vania. An aircraft came up on my TCAS [Traffic Collision Avoidance System]. He was VFR and not talking to ATC. He all of a sudden started a descent toward me. I turned. He turned. My TCAS showed our blips overlapping and a “0” for altitude difference. I guess he missed me by 50 feet. I mention this because an article on midairs, VFR flight into IMC, and usage of traffic displays might teach us a lot.
The Midair Record
“A near midair collision is defined as either an incident in which aircraft are less than 500 feet apart or...during which a pilot...feels that a hazard existed,” according to AOPA. Half of all midair collisions happen in the airport traffic pattern, AOPA reports. Of these, 80 percent oc- cur during final approach within 400 feet of the ground. The most common scenarios resulting in an airplane collision are:
• Low-wing aircraft converging with a high- wing aircraft
• One aircraft overtaking another
• Collision on final approach at a nontowered air-
port resulting from loss of situational awareness
• Formation flying and air-to-air photography
• Complacency while en route
• Mistakenly taxing onto an active runway
The MU-2 pilot’s scenario may have included some elements from the list above but appears to have been a unique set of circumstances. Virtually all inflight colli- sions happen in day visual conditions – making the MU-2 pilot’s experience very unusual.
The IFR Pilot
The MU-2 pilot was flying a very capable twin turboprop. Given the FAA’s stringent special training requirements for flying the type (14 CFR 91 Subpart N) he is likely very well trained and proficient in the Mitsubishi twin.
TCAS is a system usually installed in larger airplanes. ICAO rules require TCAS in aircraft exceeding 12,600 pounds or authorized to carry more than 19 passengers. There is no TCAS requirement for aircraft operated under
8 • TWIN & TURBINE / April 2021
conditions requiring TCAS, but it certainly could have
been voluntarily installed.
flight plan, being given descent instructions by ATC into TCAS was revolutionary when it first became available.
But traffic avoidance systems like the almost-universally required ADS-B have caught up with all but the most advanced TCAS feature: the Resolution Advisory (RA). RA not only warns of an imminent collision threat but also gives the pilot audible instructions for avoiding it – directing a climb, turn or descent to avoid the conflicting aircraft. If an RA warning is given, the pilot is expected to comply and then advise ATC. Deviating from an ATC clearance by responding to an RA collision avoidance recommendation is treated the same as maneuvering to avoid collision visually – it does not rise to the level of an emergency and is not considered a violation of an IFR clearance, but it still requires a report to controllers.
Other traffic detectors – TCAD, TIS, ADS-B – display other-aircraft locations and relative altitudes (and with ADS-B, potentially more), but they do not provide an RA in the event of a near collision. Non-TCAS traffic detec- tors do, however, give us an additional tool to detect and maneuver around other aircraft in flight.
The VFR Pilot
We don’t know anything more about the VFR pilot than what the MU-2 pilot told us: an unknown-type aircraft not in contact with ATC was descending in IMC on a course that may have led to a collision had the MU-2 pilot not maneuvered out of the way. Interestingly, the pilot of the other aircraft apparently had the MU-2 in sight of its own traffic device, assuming it was in IMC as described, or he/she made a completely coincidental turn just as the two airplanes were coming together.
It’s possible that what the MU-2 pilot interpreted as instrument meteorological conditions were seen by the VFR pilot as visual meteorological conditions. If that was the case, the VFR pilot would have been required to maintain VFR visibility and cloud clearance require- ments – generally three miles visibility and at least 500 feet below, 1,000 feet above and 2,000 feet laterally from clouds. In Class G airspace, this reduces to one-mile vis- ibility and clear of clouds.
Most pilots are taught VFR minimums exist to provide the visual pilot enough outside references to maintain spatial orientation and avoid losing control of the aircraft.