The Aircraft Prebuy Bible — What to Check Before You Buy
The definitive prebuy inspection guide: what gets checked, red flags that kill deals, negotiation tactics, and how to read a prebuy report.
Why the Prebuy Is Non-Negotiable
The prebuy inspection is the single most important step in buying a used aircraft. It costs $1,500–$3,000 but regularly saves buyers $10,000–$50,000+ by uncovering hidden problems. A prebuy found a cracked wing spar on a Bonanza that would have cost $40,000 to repair — the buyer walked away. Never skip it, never let the seller's mechanic do it, and never buy sight-unseen without one.
Finding the Right Mechanic
Use an IA (Inspection Authorization) holder who specializes in your aircraft type. A Bonanza specialist will catch things a general A&P won't. Ask the type club for mechanic recommendations. Expect $150–$200/hr labor rate for 8–16 hours depending on aircraft complexity. The mechanic should provide a written report with photos.
Engine Inspection
Compression check (all cylinders should be 70/80 or better; below 60/80 is a red flag). Borescope inspection of cylinders (check for corrosion, cracking, valve recession). Oil filter cut-open (look for metal). Oil analysis history (trending metals). Check for oil leaks, exhaust stains, cracked baffles, worn hoses, corroded fuel lines. Verify engine logbook matches installed engine (serial numbers).
Airframe Inspection
Belly corrosion (the #1 hidden killer on older aircraft). Wing spar inspection (especially Beechcraft — AD 2004-18-06). Control surface rigging and freedom of movement. Landing gear (struts, tires, brakes, wheel bearings). Skin condition (cracks, patches, repairs). Windshield crazing. Door seals. Fuel tank integrity (bladders vs. wet wing — reseal costs $5,000–$15,000).
Avionics Check
Verify all installed avionics work. Check 337 forms for all modifications. ADS-B Out compliance (mandatory since 2020). Transponder and pitot-static check currency. GPS database currency. Autopilot operation check (all modes). Intercom and audio panel. ELT battery expiration. Avionics upgrades can cost $10,000–$80,000 — know what you're getting.
Logbook Deep Dive
Complete logbooks from new are ideal. Gaps in logbook entries are red flags. Verify all AD compliance (recurring and one-time). Check 337 forms for major repairs and alterations. Look for total time discrepancies. Verify engine overhaul records (major vs. top overhaul matters). Calculate time since major overhaul (SMOH) accurately.
Damage History
Request an FAA accident/incident history search. Check NTSB records. Look for 337 forms indicating major repairs. Signs of prior damage: mismatched paint, rivet patterns that don't match factory, asymmetric gaps, and paint thickness variations. A properly repaired aircraft can be fine — an improperly repaired one is dangerous.
Common Red Flags
Missing or incomplete logbooks. Seller won't allow a prebuy or insists on their mechanic. Multiple owners in short period. Low compression on 2+ cylinders. Heavy belly or spar corrosion. AD non-compliance. Mismatched serial numbers between logbooks and nameplates. "As-is" sale with no prebuy allowed. Aircraft hasn't flown in 6+ months (corrosion risk).
Negotiating With Prebuy Findings
Every airplane has squawks — the question is how many and how expensive. Get repair estimates from the prebuy mechanic. Categorize: safety items (must fix before flight), maintenance items (should fix within 6 months), cosmetic items (nice to have). Negotiate total repair cost as a price reduction OR require seller to fix before closing. Walk away if total squawk cost exceeds 15–20% of asking price.
Reading the Prebuy Report
A good report includes: overall assessment (buy/conditional buy/walk away), compression readings with borescope photos, oil analysis interpretation, list of discrepancies with severity and estimated repair cost, AD compliance status, remaining useful life estimates for landing gear, brakes, tires, and exhaust system. If the mechanic just says "looks good" with no details, get a better mechanic.
Prebuy Cost Guide by Aircraft Type
Single-engine fixed gear (Cessna 172, Cherokee): $1,500–$2,500, 6–10 hours. Complex singles (Bonanza, Mooney): $2,000–$3,500, 10–14 hours. Light twins (Baron, Seneca): $3,000–$5,000, 12–20 hours. Turboprops: $5,000–$10,000+. Budget extra for borescope ($200–$400) and oil analysis ($30–$50).
After the Prebuy
If results are good: proceed to closing. If conditional: negotiate repairs or price reduction. If walk away: thank the mechanic, pay the bill, and move on. A failed prebuy is not wasted money — it's the best insurance you'll ever buy. The airplane you DON'T buy often saves you more than the one you do.