Hollywood, FL, USA
N131AB
PIPER PA-25-235
The pilot of the Piper PA-25 completed the local banner-tow mission and successfully released the banner. While maneuvering for landing, the airplane stalled at low altitude. The airplane was substantially damaged when it impacted flat terrain on airport property and the certificated commercial pilot sustained serious injuries. The airplane was equipped with a stall warning system that consisted of a vane-activated switch on the wing and a light in the cockpit. Electrical continuity testing and x-ray examination of the switch revealed that the internal contacts were fused, which prevented the switch from functioning in accordance with the design. The stall warning light was not illuminated at impact based on an analysis conducted by the Safety Board's Materials Laboratory. Calibration testing of the airspeed indicator revealed that the indicator read approximately 8 mph high at speeds up through at least 90 mph. The pilot had approximately 450 total hours of flight experience and approximately 130 hours in the accident airplane. Visual meteorological conditions prevailed and the reported winds were 9 knots.
**This report was modified on 4/5/2012. Please see the public docket for this accident to view the original report.** HISTORY OF FLIGHT On November 10, 2007, about 1656 eastern standard time, a Piper PA-25-235, N131AB, was substantially damaged when it impacted the ground on airport property while maneuvering for landing at North Perry Airport (HWO), Hollywood, Florida. The certificated commercial pilot sustained serious injuries. The local banner tow flight was operated by Aerial Banners Inc, and was conducted under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed. According to the Federal Aviation Administration (FAA), the flight originated at HWO, and was returning for landing after completing its banner towing mission. According to air traffic control recordings, the pilot reported to the HWO air traffic control tower (ATCT) that he was inbound for landing, and that he had obtained the current automated terminal information service (ATIS) weather and landing information. The controller instructed the pilot to report again when he reached the airport "boundary." When the flight arrived at the southwest airport boundary, the controller instructed the pilot to "proceed to the northwest corner for the north drop," and then told the pilot to plan on landing on runway 36 right. The pilot acknowledged the banner drop instruction, but questioned the controller with "that'll be a right turn for three six right?" The controller responded with "right turn between the parallels for three six right, cleared to land." According to witnesses, while headed north, the airplane dropped its banner in the assigned location west of runway 36 left, and then reversed course to the right. The airplane crossed over runway 36 left, and remained west of runway 36 right. The airplane began a left turn to align for landing on runway 36 right, then descended rapidly and impacted the ground. There was no postimpact fire. PERSONNEL INFORMATION The pilot held a commercial pilot certificate, with airplane single-engine land, multi-engine land, and instrument ratings. According to his pilot logbook, he had accumulated approximately 450 total hours of flight experience, and approximately 130 hours in the PA-25. His most recent first-class medical certificate was issued in March 2007. AIRCRAFT INFORMATION According to the type certificate data sheet, the PA-25 was a single-seat, low wing monoplane designed for aerial application of chemicals for agricultural purposes. The accident airplane was manufactured in 1965, and registered to Aerial Banners Inc in May 2004. The airplane was built and registered as a PA-25-235, but the engine installed at the time of the accident was a Lycoming O-540-G1A5, which is a 260 horsepower engine. The maintenance records did not document this airplane modification. The last 100 hour inspection was completed on September 8, 2007. The type design was no longer supported by Piper Aircraft Company; the type certificate was transferred to an Argentine company "LATINO AMERICANA DE AVIACION (LAVIA)" on April 15, 1998. METEOROLOGICAL INFORMATION The HWO 1653 surface weather observation reported winds from 340 degrees at 9 knots, clear skies, temperature 24 degrees Celsius (C), dew point 12 degrees C, and an altimeter setting of 30.04 inches of mercury. AIRPORT INFORMATION The airport was configured with four runways: 9 left, 27 right; 9 right, 27 left; 18 left, 36 right; and 18 right, 36 left. The airplane impacted in the area bounded by the four runways. Each runway was 100 feet wide and approximately 3,300 feet long. The centerlines of each pair of parallel runways were approximately 1,450 feet apart. The published traffic pattern altitude for HWO was 808 feet above mean sea level, which was 800 feet above the airport elevation. A grassy area that bounded the west edge of runway 36 left was used for banner drops, and extended approximately 1,000 feet wide in the east-west direction. WRECKAGE AND IMPACT INFORMATION According to information provided by FAA inspectors, the nose, including the engine, cowling and associated structure, exhibited crush and displacement damage. The propeller exhibited bending and chordwise scratching. The cockpit area was partially deformed. The wings were partially separated from their attach points. The left wing was crumpled and displaced aft, and the right wing had crush damage and wrinkling. The flaps were found in the retracted position. The aft fuselage and empennage appeared intact. SURVIVAL ASPECTS The pilot sustained serious head injuries. The right side of the instrument panel exhibited impact damage consistent with being struck in the aft-to-forward direction. The pilot seat remained attached to the seat tracks at all four attach points. The pilot's lapbelt restraint was intact, and the latching clasp exhibited positive engagement when tested by investigators. The cable that connected the shoulder harness to its inertia reel was fractured and separated at the swaged fitting closest to the shoulder harness webbing. The cable was examined by the National Transportation Safety Board materials laboratory, which stated the following in its report: "the broken individual wire ends...exhibited a cup and cone appearance. All features on the cable pieces were consistent with overstress separation. There was no evidence of corrosion or wear." The Safety Board was unable to determine whether the cable was an FAA-approved component, or if it was in compliance with the airplane manufacturer's design specifications. ADDITIONAL INFORMATION Pitot Tube A stainless steel tube approximately 1/8 inch in diameter served as the pitot tube. The pitot tube was bent aft, outboard, and approximately 90 degrees up from its normal orientation. The standoff distance of the pitot tube inlet below the wing surface was determined to be approximately 3 5/8 inches in its pre-accident condition. Measurements on four of the operator's other PA-25 airplanes yielded pitot tube inlet standoff distances ranging from 2 1/2 to 4 3/16 inches. Variations in standoff distances can affect the ram air pressure provided to the airspeed indicator. The Safety Board was unable to determine the airplane manufacturer's minimum or maximum standoff distances for the pitot tube, or the effect of the measured standoff distance on the accuracy of the airspeed that was presented to the pilot in the accident airplane. Airspeed Indicator The airspeed indicator (ASI) outer scale was marked as "MPH," while the inner scale was marked as "KNOTS." The white arc extended from 60 to 109 mph. The green arc extended from 67 to 124 mph, and the yellow arc extended from 125 mph to the red line at 156 mph. The airspeed arcs were congruent with the applicable airspeed limits specified in the airplane type certificate data sheet. A calibration test of the ASI was performed. The indicator was tested in 10 knot increments between 40 and 150 knots, inclusive. The ASI read higher than the input reference value at every test point. At the 60, 70, and 80 knot test points, the ASI read 68, 76, and 87 knots, respectively. Converted to mph, the test point values were 67, 78 and 89 mph, and the ASI indicated 76, 85 and 97 mph, respectively. An ASI from another of the operator's PA-25 airplanes, N169AB, exhibited values similar to those obtained on the accident airplane ASI. Stall Warning System The airplane was equipped with a stall warning system that consisted of a vane-activated switch mounted on the wing, and a light in the cockpit that was wired to the switch. Although some minor impact damage to the vane was noted, the vane moved freely. The switch was equipped with three electrical terminals labeled "COMMON, NORMALLY OPEN, and NORMALLY CLOSED." One wire was connected to the NORMALLY OPEN terminal, and one wire was connected to the COMMON terminal. The vane/switch assembly was examined by the Safety Board materials laboratory. Continuity testing of the terminals revealed that, with the vane in the spring-loaded "down" position, there was no electrical continuity between the COMMON and NORMALLY CLOSED terminals, and there was electrical continuity between the COMMON and NORMALLY OPEN terminals. This was not in accordance with the design. Electrical continuity between the terminals did not change when the switch was actuated. The switch was X-rayed to determine the relative orientation of the internal components. The materials laboratory reported that "Examination of the x-ray radiographs revealed that actuation of the switch did not change the positions of the contacts within the switch. The outer case of the vane switch was removed to examine the switch contacts. Microscopic examination of the NORMALLY CLOSED contact revealed metallic beads, consistent with incipient melting of both contact surfaces (probably due to electrical arcing). In the area of the metallic beads, the two contact surfaces appear to be welded together." The stall warning light was mounted in the center of the instrument panel. The stall warning light was examined by the Safety Board materials laboratory. The laboratory report stated that the "warning light assembly consisted of the lens, bulb, and bulb socket. There was no physical damage to the assembly. Continuity testing of the contacts on the socket found that the socket had electrical continuity and was therefore, functional. The light bulb was examined for filament stretch. The filament was intact and showed no signs of stretching." Airport Traffic Pattern Operations At the time of the accident, the ATCT was operating, and traffic was being instructed to use runways 36 left and 36 right. Normal traffic flow for these runways utilized a left-hand traffic pattern for runway 36 left, and a right-hand traffic pattern for runway 36 right. According to a statement from another banner tow pilot who flew for the same company as the accident pilot, approximately 6 days before the accident, the ATCT changed its procedures for banner tow airplanes landing on runway 36 right. Previously, after the pilots dropped their banners near the northwest corner of the airport, they were instructed to enter the right crosswind leg of a right-hand traffic pattern for landing on runway 36 right. The revised ATCT procedure instructed pilots to remain west of runway 36 right, and to fly a left-hand traffic pattern for that runway. A witness reported that the accident pilot had flown this revised pattern at least one time prior to the accident. The new ATCT-initiated traffic pattern required pilots to conduct two 180 degree turns within the 2,000 feet that separated the drop area from runway 36 right. Aerodynamic calculations showed that a single 180 degree coordinated turn at 70 mph using 30 degrees of bank resulted in a turn diameter of 1,140 feet, while a 45 degree bank decreased the diameter to 660 feet. Calculations for the same turns at 80 mph yielded turn diameters 1,500 and 900 feet, respectively. The zero-bank, flaps-retracted stall speed of the airplane was 67 mph. Aerodynamic calculations showed that in a coordinated turn using 30 degrees of bank, the stall speed increased to 74 mph. A coordinated turn using 45 degrees of bank increased the calculated stall speed to 80 mph.
The pilot's failure to maintain adequate airspeed, resulting in an aerodynamic stall. Contributing to the accident were an inoperative stall warning system and an erroneous airspeed indicator.
Source: NTSB Aviation Accident Database
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