Borescope Finding and Troubleshooting Discipline
During a routine borescope inspection of a turbofan engine's high-pressure turbine, a technician observes blade tip distress on three blades: minor material loss at the tip shroud, no cracking visible, and no evidence of overheating on adjacent vanes. The engine has 1,200 cycles since its last shop visit and is within its on-wing inspection interval. The borescope image is slightly blurred at the blade tips, and the technician is unsure whether the loss is within the manual's allowable limits. The operator's troubleshooting procedure says that tip distress within limits may be blended or left, but any cracking requires engine removal. The line station has no borescope with higher resolution, and the next borescope-capable station is a 2-hour flight away. The aircraft is scheduled for a passenger flight in 5 hours. The technician's supervisor suggests 'it looks minor, sign it off and note it.'
1. What should the technician do, and how should the troubleshooting logic be structured?
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The technician should not sign off an inspection whose result cannot be evaluated against the manual's limits. The image is blurred and the manual defines quantitative limits; without a clear comparison, the finding is indeterminate, not 'minor.' Signing it off would convert an unknown into an assumed airworthy condition.
The troubleshooting logic should proceed in order: define the symptom (tip material loss on three blades); gather evidence (clear images, blade position, cycle count, any performance shift); compare against the manual's allowable limits and criteria; and decide among outcomes - within limits and serviceable, within limits but monitor, or beyond limits requiring removal. Each branch must be tied to the manual's criteria, not to visual impression.
Because the image quality prevents step three, the correct action is to obtain a better image or escalate. Options include using a higher-resolution borescope, repeating the inspection with better lighting and positioning, or deferring the decision to a borescope-capable station. If the aircraft must fly, the decision must rest on a documented engineering or technical assessment, not a supervisor's impression. The technician should record the finding, the image limitation, and the escalation, and should not release the engine as inspected-and-clear.
2. How should the supervisor's suggestion be handled from a human factors and documentation standpoint?
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The suggestion reflects a common pressure pattern: schedule pressure plus a plausible-looking finding leads to 'sign it off and note it.' The technician should treat this as a stop signal. Human factors guidance supports challenging an instruction that would compromise an inspection result, and the organization should have a non-punitive path for doing so.
From a documentation standpoint, the record must state what was actually observed and the limitation: 'tip distress on three blades; image quality insufficient to determine limits; inspection incomplete.' That record protects the technician and gives the next station the information it needs. Recording 'minor, serviceable' would be inaccurate and would undermine later troubleshooting.
The supervisor should be brought into a documented discussion, not a corridor conversation. The technician can propose the concrete alternative - repeat with better equipment or route to the borescope-capable station - which gives the supervisor a compliant way to keep the schedule. If the flight is delayed, the delay is a consequence of an inconclusive inspection, not of the technician's caution. Organizations that punish such caution get fewer reports and more escapes, so the response should reinforce the reporting behavior.