Torque Wrench Extension and a Fuel Line Union
During a scheduled check you must torque a fuel line B-nut to 45 N·m. The only calibrated torque wrench available reads 5–60 N·m and is 400 mm long from the square drive to the centre of the hand grip. The B-nut sits in a recess, so you must fit a 100 mm crow's-foot extension in line with the wrench axis, angled so the extension continues straight along the wrench centreline. The maintenance manual states the torque figure applies to the fastener and does not mention extension use. You also note the wrench's calibration sticker expired three weeks ago, and the previous shift logged the same wrench as 'serviceable' in the tool log. Ambient temperature in the hangar is 4 °C and the task is being done outdoors on the ramp.
1. Explain how the in-line extension changes the applied torque at the fastener and state the wrench setting you would use to achieve 45 N·m at the B-nut.
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With an in-line extension, the effective lever arm increases from 400 mm to 500 mm, but the wrench still indicates torque based on its own 400 mm arm.
- Torque at fastener = Wrench reading × (effective length / wrench length)
- Required reading = 45 × (400 / 500) = 36 N·m
If the extension were fitted at 90° to the wrench axis, the effective length would be unchanged and the setting would remain 45 N·m. Because the extension is in line, the setting must be reduced to 36 N·m. This is a calculation/judgement step, not a look-up: the manual gives no extension guidance, so the mechanic must apply the lever-arm correction and record the adjusted figure.
2. Given the expired calibration and the tool-log entry, what is the correct course of action before using the wrench?
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The wrench is not airworthy for controlled torque work. An expired calibration sticker means the tool's accuracy is no longer assured and it must be withdrawn from service, quarantined, and sent for calibration. The previous shift's 'serviceable' entry does not override the calibration status - the log entry is a discrepancy that must be raised (e.g. a maintenance error report or internal occurrence report), not repeated.
Correct actions:
- Do not use the wrench for the 45 N·m task.
- Tag/quarantine the tool and route it to calibration.
- Obtain a currently calibrated wrench covering the required range.
- Record the finding and notify the supervisor so the earlier log entry can be investigated.
This tests judgement about airworthiness documentation rather than recall of a calibration interval.
3. The task is performed at 4 °C outdoors. What practical effect does this have on a hand torque application and what should you do?
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Low temperature affects both the operator and the tooling: hands lose dexterity and grip force, lubricants stiffen, and some torque wrenches are specified for a limited ambient range. The manual's torque figure is normally quoted at standard conditions; if the manual or tool specification gives a temperature limit, it must be respected. Practical actions:
- Check the wrench's specified operating temperature range; if 4 °C is outside it, do not use that wrench.
- Ensure the fastener threads and bearing faces are clean and correctly lubricated as specified - dry versus lubricated threads change the torque-to-preload relationship significantly.
- Use gloves that preserve feel, and avoid applying torque with cold-impaired grip.
- Re-check the setting after the wrench has stabilised at ambient temperature.
The key judgement is that a torque value alone does not guarantee correct preload; friction conditions and tool condition must match the manual's assumptions.