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Instructions for through-transmission inspection modes (MTTU, WTTU, ATTU).
Permitted ultrasonic instruments and specific examples used for calibration.
Recommended 1 MHz transducers and specific part numbers for inspection.
Yokes for inspection, with specific part numbers for MTTU and WTTU.
Requirement for MTTU yoke, with example part number for water supply.
Need for preamplifiers with ultrasonic instruments and examples.
Honeycomb calibration guide ST8870-1 or alternate reference standard details.
Foam tape for signal reduction, with specified type and manufacturer.
Scanning procedures for Zone 1, including calibrations and directions for honeycomb ramps.
Scanning procedures for Zone 2, including calibrations and directions for solid laminate areas.
This document outlines the procedures for the nondestructive testing of the Boeing 747's wing leading edge Krueger flaps, specifically numbers 11 and 16, using ultrasonic methods. The primary function of this manual is to guide technicians through inspections for damage, disbonds, and delaminations in these critical composite structures. The inspections are performed after the flaps have been removed from the aircraft and after any applicable service bulletin changes have been implemented.
The core function of the described procedures is to identify structural integrity issues within the Krueger flaps. This is achieved through various through-transmission ultrasonic (TTU) inspection modes: water-jet coupled Manual Through-Transmission Ultrasonics (MTTU), dry-coupled Wheel-Transducer Through-Transmission Ultrasonics (WTTU), and Air Coupled Through-Transmission Ultrasonics (ATTU). The manual emphasizes the use of computer-aided TTU (CATTU) systems for enhanced data acquisition and analysis, though it explicitly advises against the use of hand-held contact TTU for these specific procedures.
Usage features are extensively detailed, starting with the preparation of the Krueger flaps. Technicians are instructed to remove the flaps from the airplane and detach any fittings as per the relevant service bulletin. A crucial initial step involves a thorough visual inspection of the flap surfaces for cracks, particularly around fastener holes at the outboard end of the panel. This visual check extends to the inside of fastener holes to identify any disbonds or separations, with a requirement to record all such findings. The flap is then positioned on supports or a bench with its flat side down for the ultrasonic inspection.
The inspection area is clearly defined and divided into two distinct zones, each requiring a separate calibration. For MTTU inspections, open holes within the inspection area must be sealed with small pieces of tape that are transparent to ultrasound, such as mylar, teflon, or flash tape, to ensure proper water coupling.
Instrument calibration is a critical usage feature, with precise instructions for positioning the TTU device on a calibration standard. The transducers must be aligned, and the screen range adjusted to display the highest part of the TTU signal between 10 and 20 percent of full screen width. The gain is then set to bring the highest part of the signal to 80 percent of full screen height. A gate is energized and its threshold set at 20 percent of full screen height, positioned across the main part of the TTU signal. An alarm is then activated, configured to sound when the signal drops below 20 percent of full screen height. To verify calibration, the TTU device is moved over a disbond or foam tape area on the calibration standard, where the signal should diminish, and the alarm should sound. If the alarm fails to sound or if excessive noise is present, the use of a preamplifier between the receive transducer and the ultrasonic instrument's input is recommended.
The inspection procedure itself involves making scans of each inspection zone with a specified distance between scans. For Inspection Zone 1, which includes core bays and core bay ramps, the equipment is calibrated using specific positions on the standard for both bonded and disbond areas. Scans are performed on this zone, but not on solid laminate areas. For WTTU inspections, scans of honeycomb ramp areas are to be conducted in an up-and-down direction to prevent issues with wheel contact. Inspection Zone 2, covering solid laminate areas, also requires specific calibration positions for bonded and disbond areas. Scans in this zone are performed in lines parallel to the edge of the laminate area, avoiding core bays or core bay ramps.
Maintenance features, while not explicitly detailed as a separate section, are implicitly integrated into the operational guidelines. The selection of appropriate ultrasonic instruments and transducers, along with the use of specific calibration standards, ensures the accuracy and reliability of the inspection process. The manual lists several acceptable ultrasonic instruments and transducers, indicating that alternatives can be used as long as they meet the specified calibration requirements. The use of a preamplifier to address signal issues or noise also serves as a form of operational maintenance, ensuring optimal signal quality during inspections.
The calibration standard itself, either the ST8870-1 guide or an alternate reference standard with specific material and structural characteristics, is a key component in maintaining the accuracy of the inspection equipment. The alternate standard must feature a 3.0-pound nomex core with a 1-inch core depth, graphite fabric skins with a total of twelve, thirteen, or fourteen plies, and a core ramp transitioning from a core bay to a solid laminate area. The application of foam tape to the calibration standard, designed to cause a specific decrease in the received signal, is another crucial step in ensuring the system's ability to detect flaws.
Inspection results require meticulous record-keeping of all areas where the TTU signal falls below 20 percent of full screen height. The manual also addresses potential ambiguities in results, noting that some structural conditions can cause indications that might be misinterpreted as flaws. In such cases, secondary inspection procedures are recommended to further examine these indications, ensuring accurate diagnosis and preventing unnecessary interventions. This highlights a critical aspect of operational maintenance: the ability to discern true defects from benign structural features, thereby optimizing the efficiency and effectiveness of the inspection process.
General| Manufacturer | Boeing Commercial Airplanes |
|---|---|
| First Flight | February 9, 1969 |
| Role | Wide-body jet airliner |
| Range | 7, 260 nautical miles (13, 450 km) |
| Wingspan | 211 feet 5 inches (64.4 meters) |
| Length | 231 ft 10 in (70.6 m) |
| Height | 63 ft 6 in (19.4 m) |
| Cruise Speed | Mach 0.85 |
| Engines | 4 × Pratt & Whitney JT9D or General Electric CF6 or Rolls-Royce RB211 turbofans |
| Service Ceiling | 45, 100 ft (13, 700 m) |
| Crew | 2 flight crew, plus cabin crew |
