Antioch, CA, USA
N7508Y
ROBINSON HELICOPTER R22 BETA
N433JC
BEECH 35-A33
The helicopter and airplane collided midair. Both aircraft sustained minimal damage during the impact but substantial damage during the subsequent forced landings. The airplane pilot was performing a local flight and was not in contact with air traffic control (ATC) before the collision. The helicopter pilot was receiving visual flight rules flight following services from ATC throughout the flight. The helicopter pilot transitioned between two ATC sectors before the accident. On multiple occasions, the controllers for each sector misidentified the last three digits of the helicopter's call sign. Additionally, the controller in the accident sector issued a traffic advisory using the wrong call sign. Further, an aircraft with the same last three digits as the helicopter's incorrect call sign made radio contact with the controller shortly before the collision, which increased the confusion. Audio data revealed that the air traffic controller provided multiple traffic advisories to the helicopter but did not issue an alternate or immediate course of action in accordance with ATC procedures despite the fact that the aircraft's converging flightpaths had triggered the radar conflict alert system. Radar playback also revealed that, at that time, the controller was receiving a visual alert on the radar console. This alert was also observed by a controller in an adjacent approach sector who called the radar assist controller warning of the threat. The assist controller responded, "yeah, we're givin' him traffic." A few seconds later, the radar targets merged. The helicopter pilot stated that she received and complied with the traffic advisories by performing a visual scan but that, based on her communications with the air traffic controller, she did not perceive the situation to be urgent. Radar data revealed that the helicopter descended 600 feet before the collision but that the pilot did not inform the air traffic controllers about the descent. Further, as the airplane got closer and the traffic advisories were issued, the helicopter pilot began turning north, which brought the helicopter directly into the path of the approaching airplane while simultaneously placing the airplane behind her immediate field of vision. Shortly after, she sighted a silhouette of the airplane and propeller at her 4-o'clock position. She performed an evasive maneuver to the left but then felt the helicopter being struck. Neither the airplane pilot nor the occupant observed another aircraft near the airplane before the collision. Although the airplane pilot was not receiving traffic advisories from ATC, it was still the pilot's responsibility to maintain a proper visual lookout to avoid other aircraft in the area. The helicopter's left navigation light was inoperative when tested after the accident; however, this most likely did not affect the outcome because the left side of the helicopter would not have been visible to the airplane pilot at any point during the flight.
HISTORY OF FLIGHT On February 19, 2012, about 1845 Pacific standard time, a Beech 35-A33 airplane, N433JC, and a Robinson R22 Beta helicopter, N7508Y, collided midair near Antioch, California. The airplane was owned and operated by the private pilot under the provisions of Title 14 Code of Federal Regulations (CFR) Part 91 as a local flight. The helicopter was registered to Spitzer Helicopter Leasing Company and operated by the commercial pilot under the provisions of Title 14 CFR Part 91 as a solo cross-country flight in preparation for obtaining her helicopter rating. None of the aircraft occupants were injured. The helicopter was receiving flight following at the time of the accident, and departed Hayward Executive Airport, Hayward, California, about 1815, with a planned destination of Sacramento Executive Airport, Sacramento, California. The airplane departed Byron Airport, Byron, California, about 1835. Night visual meteorological conditions prevailed, and neither aircraft filed a flight plan. The airplane pilot stated that he performed an uneventful preflight inspection during which he confirmed all lights were operational. They departed Byron with the intention of performing three night landings, and 30 minutes of flight over Antioch and the Sacramento Delta area. After departure, they climbed to 2,500 feet mean sea level (msl), on a west heading. The pilot pointed out the local power station below to the passenger, and then discussed aircraft lights that he could see above and far into the distance; a few seconds later they felt a collision. Neither occupant observed another aircraft in close proximity prior to the collision, and the pilot was concerned that they may have struck a tower or bird. The airplane immediately began to shudder, and roll to the right. The pilot looked to the right wing and could see a hole, and a piece of tubing protruding from the leading edge. He established airplane control, and began a 180-degree climbing left turn to 3,000 feet. He confirmed that his landing lights were on throughout the flight. Although his transponder was switched on and set to 1200, he had not established radio contact with any air traffic control facility prior to the collision. The pilot elected to return to Byron Airport. While en route, he established radio contact with Northern California Terminal Radar Approach Control (NORCAL), who told him he had struck a helicopter. He maintained straight and level flight by utilizing continuous left aileron and rudder control inputs. During the final approach segment, the propeller speed began to decrease and he was unable to maintain altitude. As the airplane began to slow down, it began to pitch to the right despite his left control inputs. The airplane subsequently landed hard in a field short of the runway. The helicopter pilot stated that she departed Hayward with a route that was to follow highways to Concord, Antioch, and ultimately Sacramento. She contacted NORCAL Approach for flight following once she had reached Dublin, and was issued a discreet transponder code. Once over Concord, the approach controller transferred her to Travis Air Force Base Radar Approach Control. She continued the flight, and stated that a short time later she received a traffic advisory from the Travis controller. She turned on the helicopter's landing lights to increase her visibility, and began looking for the traffic (she further reported that she may have turned off the light a short time later.) She stated that based on her communication with air traffic controllers, she did not perceive the situation to be urgent. She thought she received two traffic advisories in total. The flight continued and she initiated a left turn to the north, while relaying this information to the controller. A short time later, she caught site of the silhouette of an airplane and propeller at her 4 o'clock position. She performed an evasive maneuver to the left, and then felt the helicopter being struck. She did not know the extent of the damage, and elected to immediately perform a precautionary landing. The area below was unlit and dark, and she was aware that it included significant areas of water. She therefore selected a road as her emergency landing spot. During the approach she could see multiple automobiles and diverted to a spot adjacent to the highway. She raised the collective control between 50 and 75 feet above ground level, the helicopter landed hard, and rolled onto its left side. TESTS AND RESEARCH Radar and Audio Radar data and audio recordings for the accident were provided by the Federal Aviation Administration (FAA) and United States Air Force (USAF), and reviewed by an Air Traffic Control Specialist in the NTSB Operational Factors division. A complete report is included in the public docket. The data revealed that the pilot of helicopter N7508Y initially attempted to make contact with NORCAL approach about 1821. The controller did not reply, and about 3 minutes later she made a second attempt. The controller replied utilizing the incorrect call sign of "Helicopter 7508W" and the pilot, utilizing the "08Y" call sign, requested flight following to Sacramento Executive Airport via Concord and Antioch. The controller again responded with "08W", and provided an altimeter setting. The pilot restated her call sign, and the controller responded now utilizing "08Y", expounding that her transmissions were, "fairly scratchy and hard to read." She was provided with a transponder code and the flight continued uneventfully for the next 6 minutes, after which time the controller asked her to contact Travis approach. At approximately 1832, the pilot made contact with Travis approach utilizing the call sign "Helicopter 7508Y." The controller replied with the call sign of "08W", while asking her to verify altitude. The pilot responded with an altitude of 3,000 feet and restated her call sign as "08Y", and again the controller replied with the incorrect call sign. The pilot retransmitted the correct call sign and over the next few exchanges the discrepancy was resolved, and the controller responded with the correct call sign. At 1838, the controller, once again utilizing the incorrect call sign of "08W", provided a traffic advisory to the helicopter pilot regarding a twin Cessna airplane. The pilot replied stating, "is that for 08Y?" and the controller replied in the affirmative, now utilizing the "08Y" call sign. Ninety seconds later, the controller gave a second advisory, stating that the Twin Cessna was at her 12 o'clock position, southwest bound and at 3,900 feet. A few seconds after that, the controller reported that the traffic was no longer a factor, and the helicopter continued uneventfully. Approximately 1840, a target appeared on radar approximately 11 miles southeast of N7508Y transmitting a beacon code of 1200, and an indicated mode C altitude of 1,200 feet. This aircraft was not in communication with air traffic control, and was later determined to be N433JC. About 1842, the controller asked N7508Y how much further east she would be flying, and the pilot responded, "We'll be over Antioch Bridge but be turning [.]bound soon, zero eight yankee." The radar controller responded "roger traffic one o'clock 6 miles northbound altitude indicates two thousand six hundred appears level," and the pilot replied, "zero eight yankee." Fifty seconds later, the controller advised the pilot that the target was now turning northwest bound at a range of 4 miles, and the pilot replied that she was turning northbound. Immediately following this response, an airplane with the call sign Cherokee 9808W, called the approach controller requesting visual flight rules (VFR) flight following. The controller confirmed contact, and asked the Cherokee to standby. Over the course of the next 73 seconds the controller corresponded multiple times with the Cherokee (utilizing the call sign "Cherokee 08W" and "08W") and a Piper Tomahawk (call sign 11T). Audio data revealed a beeping sound during the controller's transmissions, which was consistent with an automatically generated aural conflict alert. Radar playback data also revealed that at that time the controller was also receiving a visual alert on the radar console. During that period the Travis Approach Radar Assist controller (Radar Associate Position) received a land-line interphone call from a NORCAL approach controller who had also received the alert, and was concerned about the proximity of N7508Y and N433JC. The assist controller responded, "yeah, we're givin' him traffic." Radar data indicated that the helicopter and N433JC were now at the same altitude of 2,600 feet, within 1 mile of each other and closing. The Travis Approach controller then transmitted, "Zero eight yankee traffic now twelve o'clock less than a mile east, correction, westbound two thousand six hundred indicated." A few seconds later the radar targets merged, and the pilot of N7508Y transmitted, "MAYDAY MAYDAY HELICOPTER GOING DOWN." Examination of the radar data revealed that the helicopter's mode C reported altitude varied between 2,600 and 3,300 feet during the period it was receiving flight following. No other targets were observed in close proximity to the two aircraft leading up to the collision. Interpretation of the voice recordings revealed that although the helicopter pilot always reported her correct call sign, background noise and the inflection of her voice often resulted in the last digit, "yankee" sometimes sounding like "whiskey." Airframe Examinations Postaccident examination of the airplane revealed that a forward portion of helicopter's right skid had become lodged in the leading edge of the right wing, midspan. A 6-inch-long section of one propeller blade tip was missing, and the spinner sustained crush damage and a black paint transfer next to the back plate. During the forced landing the airplane sustained substantial damage to the wingtips, firewall, and the fuselage just aft of the left wing trailing edge. The helicopter sustained damage during the collision sequence limited to the forward right skid, and the center section of the left skid, which was not recovered. The helicopter did not sustain damage during the collision, which would have prevented normal flight. The helicopter rolled over during the landing, most likely because of the separated landing gear skids. As it rolled, the tailcone came away from the fuselage, and the forward cabin struck the ground. The landing light switch was found in the "OFF" position following the accident, and subsequent testing revealed that the lamp was operational. The rear (white) and right (green) navigation lamps illuminated when tested, however, the left (red) lamp did not light. Examination of the filament revealed that it had broken away completely at both posts. Additional Information FAA Order JO7110.65U prescribes air traffic control procedures and phraseology for use by persons providing air traffic control services. According to the order, "Controllers are required to be familiar with the provisions of this order that pertain to their operational responsibilities and to exercise their best judgment if they encounter situations that are not covered by it." The order contains the following applicable excerpts: "Section 2-1-1, ATC SERVICE: The primary purpose of the ATC system is to prevent a collision between aircraft operating in the system and to organize and expedite the flow of traffic, and to provide support for National Security and Homeland Defense. In addition to its primary function, the ATC system has the capability to provide (with certain limitations) additional services. The ability to provide additional services is limited by many factors, such as the volume of traffic, frequency congestion, quality of radar, controller workload, higher priority duties, and the pure physical inability to scan and detect those situations that fall in this category. It is recognized that these services cannot be provided in cases in which the provision of services is precluded by the above factors. Consistent with the aforementioned conditions, controllers must provide additional service procedures to the extent permitted by higher priority duties and other circumstances. The provision of additional services is not optional on the part of the controller, but rather is required when the work situation permits." Section 2-1-2, DUTY PRIORITY: Give first priority to separating aircraft and issuing safety alerts as required in this order. Good judgment must be used in prioritizing all other provisions of this order based on the requirements of the situation at hand." 2-1-6, SAFETY ALERT: Issue a safety alert to an aircraft if you are aware the aircraft is in a position/altitude which, in your judgment, places it in unsafe proximity to terrain, obstructions, or other aircraft. Once the pilot informs you action is being taken to resolve the situation, you may discontinue the issuance of further alerts. Do not assume that because someone else has responsibility for the aircraft that the unsafe situation has been observed and the safety alert issued; inform the appropriate controller. NOTE- 1. The issuance of a safety alert is a first priority (see para 2-1-2, Duty Priority) once the controller observes and recognizes a situation of unsafe aircraft proximity to terrain, obstacles, or other aircraft. Conditions, such as workload, traffic volume, the quality/limitations of the radar system, and the available lead time to react are factors in determining whether it is reasonable for the controller to observe and recognize such situations. While a controller cannot see immediately the development of every situation where a safety alert must be issued, the controller must remain vigilant for such situations and issue a safety alert when the situation is recognized. 2. Recognition of situations of unsafe proximity may result from MSAW/E-MSAW/LAAS, automatic altitude readouts, JO 7110.65U 2/9/12 ....... b. Aircraft Conflict/Mode C Intruder Alert. Immediately issue/initiate an alert to an aircraft if you are aware of another aircraft at an altitude which you believe places them in unsafe proximity. If feasible, offer the pilot an alternate course of action. c. When an alternate course of action is given, end the transmission with the word "immediately." Section 2-4-15, EMPHASIS FOR CLARITY: Emphasize appropriate digits, letters, or similar sounding words to aid in distinguishing between similar sounding aircraft identifications. Additionally: a. Notify each pilot concerned when communicating with aircraft having similar sounding identifications. b. Notify the operations supervisor-in-charge of any duplicate flight identification numbers or phonetically similar-sounding call signs when the aircraft are operating simultaneously within the same sector."
The failure of both pilots to see and avoid the other aircraft during cruise flight. Contributing to the accident was the failure of air traffic control personnel to issue the helicopter pilot with a prompt and appropriate alternate course of action upon receiving a conflict alert.
Source: NTSB Aviation Accident Database
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