1. Running Head: HETEROGENOUS AIRCRAFT USE AIRSPACE EFFECTS 1
HETEROGENOUS AIRCRAFT USE AIRSPACE EFFECTS AND ACCIDENT
INVESITGATION
by:
Aaron Lancaster
SFTY 330: Aircraft Accident Investigation
Embry-Riddle Aeronautical University
Worldwide Campus
November 2011

2. HETEROGENOUS AIRCRAFT USE AIRSPACE EFFECTS 2
Heterogenous Aircraft Use Airspace Effects
Can you imagine encountering another aircraft while flying your own only to realize that
it is very different from your own – perhaps even unmanned? How would you react? The thought
of operating diverse aircraft in close proximity can be daunting. The operational environment of
heterogenous-use airspace is very challenging to modern air traffic.
The U.S. National Airspace System (NAS) encompasses a wide array of airspace classes
and aircraft of various categories, classes and types. From sparely occupied, uncontrolled
airspace to the busiest Class B airspace surrounding airports accommodating international traffic,
the NAS brings into proximity a wide variety of aircraft operating under different sets of rules
and regulatory principles (FAR/AIM, 2011).
The complexity of the NAS brings heterogeneous traffic together at airport nodes (IPH,
2011). By nature, these centers of activity result in increased traffic density and necessitate the
use of special precautions to ensure deconfliction.
For the purposes of this paper, Heterogenous Use Airspace (HUA) will be used to refer to
the condition of any contiguous part of the National Airspace System (NAS) wherein dissimilar
aircraft are operating. For the purposes of this paper it will be assumed that all airspace is
heterogenous unless otherwise specified in nature and NAS will be used interchangeable with
HUA.
Description & Applications
The U.S. National Airspace System
The U.S. National Airspace System (NAS) encompasses all elements of the aeronautical
network that permit and enable aviation commerce. These elements include: U.S. airspace,

3. HETEROGENOUS AIRCRAFT USE AIRSPACE EFFECTS 3
aeronautical navigation aids, equipment, services, airports and landing sites, charts, information
and notices, rules and regulations, procedures, technical data, manpower, and material (IPH,
2011).
The NAS is structured to provide adequate control of air traffic based on density and
flight rules in use. In the most traffic-dense areas, Class B airspace, traffic is not permitted to
operate within 30nm of the airport without an operational Mode-C Transponder. While the
description and details of operation of Mode-C and Secondary Surveillance Radar (SSR) are
beyond the scope of this paper. Briefly, Mode-C transponders work in conjunction with SSR and
Traffic and Collision Avoidance Systems (TCAS) as a tool for Air Traffic Control (ATC) and
pilots to ensure separation of air traffic. Additionally, aircraft are prohibited from entering Class
B airspace without clearance. At the time of this writing only 12 airports within the U.S. have
Class B airspace (FAR/AIM, 2011).
Procedures and precautions are used in Class B as well as other controlled airspace
classes to ensure separation of traffic operating under Instrument Flight Rules (IFR) from that
operating under Visual Flight Rules (VFR). The Class B airspace will normally encompass all
IFR approaches published pertaining to the airport in reference (FAR/AIM, 2011). Where less
stringent classes of airspace are employed, controlled airspace is generally used to gain and
maintain control of approach and departure areas. Commonly, Class E airspace is employed to
form an “Extension Area” of another airspace such as a Class D area (FAR/AIM, 2011).
Diverse Aircraft
As previously mentioned, aircraft range widely in category, class, and type. These
parameters distinguish aircraft from each other. There are seven (7) possible categories of
aircraft: Airplane, rotorcraft, glider, lighter-than-air, powered-lift, powered parachute, or weight-

4. HETEROGENOUS AIRCRAFT USE AIRSPACE EFFECTS 4
shift control aircraft (FAR/AIM, 2011). The class of an aircraft is a sub-type on the aircraft's
category. In the case of the aircraft being in the airplane category it could be either a single- or
multi-engine as well as either a land- or sea- plane for a total of four possible combinations
(FAR/AIM, 2011). Rotorcraft category aircraft may be either a helicopter or gyroplane. Type
ratings may include aircraft such as large aircraft, turbojet-powered airplanes, and other FAA
Specified aircraft (FAR/AIM, 2011).
A new type of aircraft entering the General Aviation (GA) community is the Unmanned
Aerial System (UAS). UASs are currently being used by the U.S. DOD, NASA, DHS, and other
federal, state, and local agencies to perform surveillance, research, security, and other operations
(UAS FAQ, 2011). The DOD and FAA are currently working together to develop plans,
procedures, and implementations of UASs into the NAS (OSD, 2010).
There are two main problems with UAS operations in an otherwise manned-aircraft
world. First, UASs do not have eyes-out capability with which to “see-and-avoid” other aircraft.
Second, there is potential for loss of control data link with the UAS ground station as well as
other aircraft in the vicinity. Some work has been done to equip future generations of UASs with
a “sense and avoid” capability (OSD, 2010). that will enable and alert the remote UAS operator
to other aircraft in vicinity of the UAS, however all but the most technologically advanced UASs
are not yet equipped (MIT, 2011). Because of this special procedures must be followed whenever
a UAS is flown outside restricted airspace, established by the UAS operator first obtaining a
Certificate of Approval (COA) from the FAA (Flightfax, 2006).
Air Traffic Control
Simply stated, "The prime objective of air traffic services, as defined in the Annex, is to
prevent collisions between aircraft, whether taxiing on the, maneuvering area, taking off,

5. HETEROGENOUS AIRCRAFT USE AIRSPACE EFFECTS 5
landing, en route or in the holding pattern at the destination aerodrome" (ICAO, ANNEX 11).
Air Traffic Control (ATC) will take measures necessary to accomplish this objective such as
aircraft separation through traffic advisories, flight following, and positive control. Avoiding
collisions between aircraft centers around maintaining “aircraft separation” well before a
problem emerges.
ATC relies on technological aids to accomplish its purpose effectively beyond the Line-
of-sight with the naked eye. Binoculars are effective to a point but beyond that ATC relies
heavily on Secondary Surveillance Radar (SSR) to gain needed information to keep aircraft
separated (ASR-11, 2011). SSR provides position, altitude, and heading information through
reports from on-board aircraft transponder systems. This information is then displayed
graphically for controllers' use. Availability of these systems depends on the area of operation.
They are generally available within 30nm of Class D or larger airspace.
HUA Implications
In this part we will look at HUA implications from an investigators standpoint. This
paper will focus primarily on the HUA accident causes which stem from the nature the diverse
aircraft using the same airspace. Additionally, we will look at some of the complications
surrounding investigations of HUA accidents. Finally, we will look at FAA and NTSB guidance
established as a result of HUA accidents.
Regulation & Operation of HUA
The FAA has provided clarification that their position concerning the use of the NAS is to
promote use by all parties involved rather than creating different airspace types for diverse
aircraft. In the FAA's words, “Currently there are no actions being taken to establish a "special
UAS airspace". This "special UAS airspace" would be counter to the idea of integrating
unmanned aircraft into the NAS because it would be segregating, not integrating.” (UAS FAQ,

6. HETEROGENOUS AIRCRAFT USE AIRSPACE EFFECTS 6
2011). It is clear from the information available on their website the FAA intends for the NAS to
remain public-use airspace open to all who would use it for commerce, business, or pleasure.
Proposals have been made to create airspace that would separate manned aircraft from
unmanned aircraft (Minoz, 2011). Although this would add an additional layer of safety, it does
not make good use of the public NAS. Additionally procedures related to passing through a UAS
layer could result in additional accidents. This does option is not appealing to many.
HUA Use & Implications
While efficient airspace use drives HUA, aircraft systems must be adapted for safe
operation. Low-cost technological solutions such as Traffic Alert and Avoidance Systems
(TCAS) are now available which enable manned aircraft to avoid other aircraft. Increased
situational awareness is needed on the part of the aircrew to ensure collision avoidance. This
encompasses greater capacity to absorb and process information in addition to greater levels of
the kind of information needed.
HUA Incidents & Accident Investigations
There are two main incidents resulting from HUA since 2009. In these incidents the
nature of heterogenous aircraft was a significant finding of the incident investigation.
Incident #1: The first incident we will look at is the August 8, 2009 mid-air collision of
N401LH, a Eurocopter AS350BA helicopter, and N71MC, a Piper PA-32-300 single-engine
plane over the Hudson River near Hoboken, NJ. This accident resulted in the death of the pilot
and five passengers of the Eurocopter and the pilot and two passengers of the Piper (“AAR10-
05”, 2010). In this incident the AS-305 departing from a heliport near Hoboken, NJ was climbing
through 1,100ft. MSL when it was struck from the 4 O'Clock position by the Piper who was in
“straight and level” flight at 1,100ft. MSL. It is unknown whether or not the Piper pilot saw the
helicopter. However, the Eurocopter was equipped with high visibility rotor blades, strobe anti-
collision lights, and pulsating landing and taxi lights (“AAR10-05”, 2010). It was also

7. HETEROGENOUS AIRCRAFT USE AIRSPACE EFFECTS 7
determined by accident investigators that both aircraft were equipped with FAA Traffic
Information Service (TIS) receivers. TIS provides information on other aircraft in vicinity (7nm
and +/- 3,000ft. ALT) every 5 seconds to pilots via cockpit display systems (“AAR10-05”, 2010).
Although the responsibility to “see-and-avoid” other aircraft is that of the pilot, ATC will
assist in this responsibility. In the case of this accident there was an error in the hand-off of
controllers pertaining to the Piper. The pilot was given the proper frequency for the receiving
controller. However the Piper pilot's read back was incorrect. The releasing controller did not
recognize and correct this due to a simultaneous land-line telephone call unrelated to the
performance of his duties. The Piper pilot never contacted the receiving controller (“AAR10-05”,
2010).
Additionally, the pilot of the Piper would have only had 32 seconds before the collision to
detect and avoid the Eurocopter. Given the complex back ground of the buildings in the area and
the relatively small and slow moving silhouette of the Eurocopter the Piper pilot would have had
a difficult time seeing the helicopter (“AAR10-05”, 2010).
The NTSB determined two probable causes for this accident. First, the inherent
limitations of the “see-and-avoid” concept coupled with the lack of use of supplemental
technologies did not permit the pilots to maintain aircraft separation. Second, the ATC
controller's lack of procedural and professional discipline in combination with being distracted
led to the crash (“AAR10-05”, 2010).
Five safety recommendations resulted from this investigation. First, the obvious issue of
ATC procedures and professionalism when performing duties. Second, Special Flight Rules Area
(SFRA) procedures were clarified. Third, changes to the Hudson River SFRA were
recommended. Forth, previous guidance on the “see-and-avoid” concept (AC 90-48(C)),

8. HETEROGENOUS AIRCRAFT USE AIRSPACE EFFECTS 8
published in 1984, were revisited. Fifth, additional information on helicopter Electronic Traffic
Advisory Systems was given (“AAR10-05”, 2010).
Incident #2: The second incident we will look at is the December 31st
, 2010 crash of N2876L,
a Cessna 172H, mid-air collision with N312PH “AirCare 5”, a Eurocopter EC135-P2, in the
traffic pattern of the Shenandoah Valley Regional Airport (SHD), Wyers Cave, VA. In which, the
pilot and passenger of the Cessna were fatally injured (“ERA11FA101A”, 2011).
In this accident “AirCare 5” entered the traffic pattern after identifying two other aircraft
in the pattern. Both of these aircraft were small airplanes. The pilot did not identify any other
aircraft in the vicinity, either visually or on the Eurocopter's Skywatch Traffic Collision
Avoidance Device (TCAD), a TCAS (“ERA11FA101A”, 2011). After entering the traffic pattern,
the pilot saw the wing of the Cessna underneath his aircraft and even though he attempted to
climb the Cessna struck the skids of the helicopter.
It was later found that the TCAD did not ID and display the Cessna. This was verified by
the three crew members aboard who were trained in the use of the TCAD (“ERA11FA101A”,
2011). Both the Eurocopter and the Cessna were equipped with radios and transponders.
However, the initial findings do not indicate if the Cessna's transponder might have been
operational or not at the time of the accident.
The preliminary report indicates that the right wing was separated during the collision
and was found approximately 700 ft. prior to the remainder of the wreckage (“ERA11FA101A”,
2011). The main wreckage was found near an impact crater where one propeller blade was found
buried. Additionally, the engine and remaining propellor blades were found nearby separated
from the airplane firewall. The main wreckage was found immediately beyond the crater,
inverted. The wreckage was described by the NTSB as, “severely deformed and coiled over itself

9. HETEROGENOUS AIRCRAFT USE AIRSPACE EFFECTS 9
due to impact forces.” (“ERA11FA101A”, 2011)
As this report is preliminary information, the NTSB did not make any recommendations.
This accident brings to light the previously stated limitations of the “see-and-avoid” concept.
Additionally, it also sheds light on the limitations of supplemental TCAS technologies. Primarily,
if other aircraft in the vicinity are not utilizing transponders properly TCAS will not provide
alerts to their presence.
Another factor of note is the use of the same traffic pattern altitude by both fixed- and
rotor-wing traffic. Though not operating under FAR Part 91 rules at the time, it is generally
considered “best-practice” for helicopters to avoid the flow of fixed-wing traffic whenever
possible (FAR/AIM, 2011). Had the helicopter been under Part 91 rules at the time it may have
been in violation of that part because it was in the flow of traffic even though the pilot claims to
not have been at traffic pattern altitude (“ERA11FA101A”, 2011).
Conclusion
In this paper we have seen how various incidents demonstrate that the heterogenous use
of airspace has many complexities. The addition of unmanned aircraft systems stands to further
compound the complexities of HUA. The limitations of the “see-and-avoid” concept echo
throughout incidents like those examined here. Human error on both the part of pilots and air
traffic controllers creates break-downs in the already complex system and leads to accidents. In
order to overcome the potential dangers presented by the heterogenous nature of the NAS
operational environment we must use regulation, procedures, and technology to prevent
accidents from occurring that result in loss of life.

10. HETEROGENOUS AIRCRAFT USE AIRSPACE EFFECTS 10
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11. HETEROGENOUS AIRCRAFT USE AIRSPACE EFFECTS 11
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