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Safety Recommendation Details

Safety Recommendation A-68-033
Details
Synopsis: OUR RECENT INVESTIGATION OF THE NORTHEAST AIRLINES, INC., FH-227C, N-380NE ACCIDENT, NEAR HANOVER, NEW HAMPSHIRE, ON OCTOBER 25, 1968, HAS DISCLOSED SEVERAL AREAS WHERE IMPROVEMENTS TO AVIATION SAFETY ARE NEEDED. OUR INVESTIGATION HAS INDICATED THAT THE POSSIBILITY EXISTS THAT THE NORTHEAST ACCIDENT FLIGHT EXPERIENCED FALSE INDICATIONS OF STATION PASSAGE WHILE MAKING A VOR APPROACH FOR LANDING AT THE LEBANON AIRPORT.
Recommendation: WE WOULD, THEREFORE, RECOMMEND THAT THE FAA CONDUCT LONG TERM RADIO FREQUENCY MONITORING OF THE LEBANON VOR AREA FOR SIGNAL INTERFERENCE. THE BOARD RECOMMENDS THAT PRIORITY CONSIDERATION BE GIVEN TO THE INSTALLATION OF DUAL NAVIGATIONAL FACILITIES AT THOSE LOCATIONS WHERE A SINGLE FACILITY COULD EXHIBIT CHARACTERISTICS OF THE TYPE FOUND DURING OUR INVESTIGATION OF THE LEBANON ACCIDENT. THE BOARD RECOMMENDS THAT A REVIEW BE MADE OF THE DESIGN CONCEPT OF THE WILCOX MODEL 806A RECEIVER AND ITS COMPATIBILITY WITH OTHER AIRBORNE INSTRUMENTATION AND GROUND STATION NAVIGATIONAL EQUIPMENT TO ASSURE STANDARDS OF AIRWORTHINESS. FURTHERMORE, THE FACTS DISCLOSED DURING OUR INVESTIGATION OF THIS ACCIDENT INDICATE TO US THAT THIS COMPATIBILITY PROBLEM MAY BE GENERAL IN NATURE AND THAT CONSIDERATION SHOULD BE GIVEN TO REVIEWING ALL PERTINENT STANDARDS FOR COMPATIBILITY OF GROUND AND AIRBORNE NAVIGATION COMPONENTS. FAA SHOULD PROVIDE THE LEADERSHIP IN DEVELOPING AND IMPLEMENTING AN INDUSTRYWIDE OPERATIONAL INCIDENT REPORTING SYSTEM FOR THE INTERIM PERIOD. IN MOVING TOWARD THIS OBJECTIVE, WE WOULD HOPE THAT YOU WOULD GIVE EARLY ATTENTION TO INSURING A WIDER DISSEMINATION OF EXISTING OPERATIONAL INCIDENT DATA AMONG THE ELEMENTS OF YOUR ORGANIZATION. OUR FINAL RECOMMENDATION CONCERNS THE REEMPHASIS OF WHAT COCKPIT INDICATIONS CONSTITUTE POSITIVE STATION PASSAGE DURING A VOR INSTRUMENT APPROACH.
Original recommendation transmittal letter: PDF
Overall Status: Closed - Acceptable Action
Mode: Aviation
Location: Hanover, NH, United States
Is Reiterated: No
Is Hazmat: No
Is NPRM: No
Accident #: DCA69A0004
Accident Reports: Northeast Airlines, Inc., Fairchild Hiller FH-227C, N380NE
Report #: AAR-70-07
Accident Date: 10/25/1968
Issue Date: 12/5/1968
Date Closed: 9/16/1969
Addressee(s) and Addressee Status: FAA (Closed - Acceptable Action)
Keyword(s):

Safety Recommendation History
From: FAA
To: NTSB
Date: 1/14/1969
Response: 1. SIGNAL INTERFERENCE EFFECTS ON THE LEBANON VOR FACILITY. WE HAVE INVESTIGATED THE POSSIBILITY OF RADIO FREQUENCY INTERFERENCE EFFECTS AT LEBANON FROM CO-CHANNEL STATIONS. DATA DERIVED IN COORDINATION WITH ESSA, U. S. DEPARTMENT OF COMMERCE, SHOWS THAT, CONSIDERING DUCTING AND SUPEREFRACTION, THERE IS ONE CHANCE IN FIFTY THAT A MAXIMUM SIGNAL OF TEN MICROVOLTS COULD BE RECEIVED IN THE LEBANON AREA FOR A TOTAL OF 50 MINUTES A YEAR FROM THE NEAREST CO-CHANNEL VOR AT ELMIRA, NEW YORK. THIS SIGNAL WOULD BE USABLE ONLY IN THE ABSENCE OF THE LEBANON VOR, BUT WOULD BE ABOUT 20 DECIBEL LOWER THAN THE LEBANON VOR SIGNAL IN THE FLIGHT AREA IN QUESTION. THIS RATIO WOULD CAUSE LESS THAN ONE DEGREE OF ERROR. EXTENSIVE TESTS CONDUCTED AT LEBANON INDICATED THE CLARKSBURG EFFECT TO BE QUITE PREVALENT IN THE LEBANON AREA. THIS EFFECT RESULTS FROM THE PRESENCE OF LOW- FREQUENCY SIGNALS (5 HZ TO 20 HZ) IN THE RECEIVER INDICATING CIRCUITS. THE SIGNALS ARE THE RESULT OF THE AIRCRAFT PASSING THROUGH A REGION WHERE THE VOR DIRECT SIGNAL INTENSITY IS ALTERED BY SIGNALS FROM A REFLECTING SURFACE. THE ACTUAL LOW FREQUENCY SIGNALS GENERATED BY THIS ACTION IS A FUNCTION OF THE AIRCRAFT'S GROUND SPEED AND ITS VARYING ANGULAR RELATIONSHIP TO THE UPWARD REFLECTED SIGNAL. THEREFORE, THE IRREGULAR OCCURRENCE OF DEVIATIONS FROM THE CLARKSBURG EFFECT IS EXPLAINABLE AND WE CANNOT CONCLUDE THAT RF INTERFERENCE IS INDICATED. HOWEVER, WE WILL GIVE FURTHER CONSIDERATION TO THE NEED FOR THE RECOMMENDED LONG TERM FREQUENCY MONITORING. PERFORMANCE OF RECEIVERS WHICH EXCLUDE THE EFFECT BY MEETING THE STANDARD OF AC 91-18 WILL BE A FACTOR IN THIS DETERMINATION. 2. NEED FOR ADDITIONAL NAVIGATION FACILITIES AT LEBANON. THE FAA HAS A POLICY TO IMPROVE NAVIGATION AIDS WHEN NECESSITATED BY UNSATISFACTORY PERFORMANCE. IN THE CASE OF VOR THIS USUALLY INVOLVES RELOCATION OR CONVERSION TO DOPPLER VOR. IN ANY EVENT, AN ADDITIONAL NAVIGATION AID SUCH AS DME IS PRIMARILY INSTALLED TO PROVIDE ADDITIONAL OPERATIONAL BENEFITS, I.E., LOWER LANDING MINIMA OR REDUCTION OF FLIGHT TIME, RATHER THAN SUPPORT OF FACILITIES HAVING UNSATISFACTORY PERFORMANCE. THE FLIGHT INSPECTION TOLERANCES SPECIFIED FOR VOR FACILITY PERFORMANCE IN THE UNITED STATES STANDARD FLIGHT INSPECTION MANUAL (USSFIM) CONFORM TO INTERNATIONAL STANDARDS AND ARE ADEQUATE TO SUPPORT THE VOR INSTRUMENT APPROACH PROCEDURES. THE LEBANON VOR PERFORMS WITHIN THESE TOLERANCES AND, THEREFORE, SHOULD NOT REQUIRE AN ADDITIONAL FACILITY TO SUPPORT THE INSTRUMENT PROCEDURE. NOTWITHSTANDING BUDGETARY CONSTRAINTS, WE WOULD LIKE TO SEE A DME LOCATED AT EVERY VOR SITE. HOWEVER, OUR ULTIMATE OBJECTIVE IS TO PROVIDE VERTICAL GUIDANCE, AS WELL AS DIRECTIONAL, AT ALL AIR CARRIER AIRPORTS. 3. OPERATING CHARACTERISTICS OF THE WILCOX 806A NAVIGATION RECEIVER. WILCOX ELECTRIC COMPANY IS NOW DEVELOPING A DESIGN CHANGE TO THEIR EQUIPMENT TO MINIMIZE THE DIFFICULTIES EXPERIENCED DURING FLIGHT CHECKS AT LEBANON. THE RESTRICTION DISCUSSED ABOVE ON THE MODEL 806ARECEIVER WILL BE RESCINDED WHEN THE EQUIPMENT HAS BEEN MODIFIED. WE