Commercial Fixed Wing
Air Traffic Control Fully Certified
Air Traffic Control Radar 2; Air Traffic Control Time Certified In Pos 1 (yrs) 2
Workload; Other / Unknown
ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Flight Crew Took Evasive Action
Airspace Structure
MDT is a level 7 Combined Tower with Radar/TRACON. The airport and surrounding airspace is Class Delta with an overlying TRSA. Although MDT is not as busy as some major airports in the US; there are several times during the day where commercial/corporate traffic is considerable; typically alternating between waves of IFR arrivals and departures. The traffic levels and passengers enplanements are well above the threshold for Class Charlie airspace; but the airport retains an outdated and inherently unsafe combination of Class Delta and TRSA airspace. The primary reason for this report aims to address the unsafe condition which exists at MDT created by the lack of class Charlie airspace. MDT Class Delta airspace extends from the surface to 2;800 FT MSL; with typical lateral dimensions. In addition; it is combined with the nearby CXY airport Class Delta airspace; which in itself creates a more complicated airspace structure in the area. It is not uncommon for VFR traffic in the vicinity of MDT to overfly the airport and surrounding areas at altitudes as low as 3;000 FT MSL; some even to the very lowest they can to remain above the MDT Class Delta. This is particularly unsafe as MDT departures are vectored out of MDT with an initial climb to 3;000 FT MSL; and these VFR aircraft are under no obligation to participate in the ATC system while in the overlying TRSA airspace. Not only that; but these same VFR targets will often unknowingly be on the MDT final approach path (which can often extend to 15+ miles) at altitudes that are in direct conflict with arrival aircraft. This is again particularly unsafe as two way radio communication is not required of these aircraft which often leaves the Controllers and Pilots of MDT arrivals guessing at what these targets will do. There have been repeated TCAS RAs issued to aircraft that are departing from or arriving to MDT; even if the controllers working at the time can identify the potential conflicts. The proximity of the IFR departures and arrivals to these non-participating VFR targets is unacceptable and risk prone; especially at an airport where the commercial/corporate traffic is predictably elevated at certain times of the day. In the best case scenario; IFR aircraft (including commercial traffic) is being held on the ground (or vectored off on approach) to avoid conflicts with traffic since ATC cannot be certain of its movement. In the worst cases; traffic in being put into a situation where evasive action is required to avoid NMAC proximity. The implications for traffic without a TCAS system is obvious; and serious. Class Charlie airspace would allow controllers to predict and control the path and altitude of any aircraft that is transitioning this airspace; and prevent these uncontrolled airplanes from stopping departures; arrivals; and causing much larger aircraft from making abrupt evasive maneuvers. Pilots of the non-participating aircraft are also at risk; whether they are aware of their location or not. It may be deceptive to GA pilots and similar users who are looking at the sectional chart and seeing only Class Delta airspace when in reality MDT is far busier and has far more passenger enplanements than a large amount of already established Class Charlie airports in the NAS. This is particularly relevant on days where VMC prevails and a large increase in VFR flights occurs. So many airports that are far slower than MDT with far less commercial traffic have Class Charlie airspace; yet MDT does not. This issue has been reported (mandatorily when the situation requires it) and voluntarily several times. Even if these events do not occur daily; we are trying to convey how easily a very dangerous situation could develop. We are always learning from the past in aviation; and in this case; the problem we are facing is not new; and has caused serious (sometimes fatal) incidents in other locations in the NAS.
MDT Controller reported numerous conflicts and delays have resulted due to traffic density; complexity; type; and airspace design.  Reporter recommended airspace be classified as Charlie for safety.