FAA Part 135 Certificate Action Letter of Investigation Response

The situation

Mike, 44, owns Piedmont Air Charter, a Part 135 on-demand charter operator in Charlotte, NC, with 4 aircraft (2 Cessna Citations, 2 King Airs), 11 employees. He's been operating for 9 years with a clean safety record.

In November 2025, Piedmont flew a last-minute charter flight using a pilot who had exceeded his 14 CFR § 135.265 flight time limitations for the week, the pilot's flight time was accurately logged, but when a client called at 10 PM for an emergency next-morning flight, Mike's dispatcher had failed to run the duty-time check through Piedmont's scheduling system.

In January 2026, the Charlotte FSDO sent an LOI asking Mike to explain the circumstances of the flight.

Mike has 30 days to respond. He knows what happened (a dispatch error, not an intentional violation). But he doesn't know: Is it better to respond or exercise the informal conference privilege? What does FAA Order 2150.3C say about mitigating factors? Will responding in writing lock him into a version of events? What's the difference between an Administrative Action (warning notice, letter of correction) vs. legal enforcement proceeding?

An aviation attorney quoted $8,500 for "LOI response and FSDO conference representation." Mike's insurance covers some costs but the $8,500 comes out of company cash flow during a slow season.

Who receives this

Part 135 on-demand charter operators (1-10 aircraft), small Part 91 Subpart K fractional operators, and small air ambulance operators receiving FSDO Letters of Investigation for flight operations, crew rest, maintenance record-keeping, and drug/alcohol testing violations. Primary concentration: Southeast, Southwest, and Mountain West FSDO regions (highest density of small on-demand charter operators).

Why the agency will not advise you

The FSDO inspector who issues the LOI is investigating a potential violation on behalf of the FAA, they cannot advise the certificate holder on how to respond to their own LOI. FAA Order 2150.3C (Compliance and Enforcement Program) and the FAA Compliance Philosophy documents lay out exactly the mitigation factors FAA considers, applying them to a specific case is the value.

Key facts, with sources

• FAA's enforcement process begins with a Letter of Investigation (LOI) issued by the Flight Standards District Office (FSDO) when an inspector has identified a potential violation. The LOI asks the certificate holder or airman to explain the circumstances. Part 135 air carrier certificates are subject to operations specifications (OpSpecs) that define the carrier's authorized operations. Common Part 135 LOI triggers: (1) deviations from OpSpecs (conducting operations outside authorized aircraft types, flight paths, or conditions); (2) crew flight time and duty period violations (14 CFR § 135.265-271); (3) maintenance record-keeping deficiencies (14 CFR § 135.411); (4) drug and alcohol testing program violations (14 CFR Part 120); (5) charter flights conducted without proper Part 135 authority (dry lease vs. wet lease ambiguity). FAA Order 2150.3C (FAA Compliance and Enforcement Program) governs the process: LOI to investigation to either administrative action (warning notice, letter of correction) or legal enforcement (civil penalty, certificate suspension/revocation proceedings). Part 135 enforcement actions number ~300-600/year across ~3,000 active certificates. Source: FAA Compliance and Enforcement — 14 CFR Part 13 · FAA Order 2150.3C — Compliance and Enforcement Program · Part 135 Air Taxi & Commercial Operators — FAA
• The Part 135 certificate holder market includes ~3,000 active certificates, ranging from single-aircraft air taxi operators to mid-size air ambulance and charter companies. Most operators with 1-5 aircraft are small businesses that lack in-house legal counsel. Aviation defense attorneys at aviation law firms (Shackelford Law, Aiken, Gump, Alexander + Cleaver) charge $300-$500/hour; a typical LOI response engagement costs $5,000-$10,000 (2-3 days of attorney work). AOPA's Legal Services Plan covers individual airmen's pilot certificate actions but does NOT cover Part 135 certificate holder (operator) enforcement actions. No self-serve FAA LOI response tool found. Source: AOPA Legal Services Plan — Coverage Overview · FAA Enforcement Process — Pilot Legal Questions

When to bring in a professional

Self-serve responses fit routine cases: clear facts, amounts a business can absorb, and a deadline still ahead of you. Bring in a licensed professional when the amount at stake is large relative to their fee, the facts are genuinely disputed, criminal exposure is possible, or the deadline has already passed. A short paid consultation to sanity-check your plan is often worth it even when you handle the filing yourself.

All sources for this guide

1. FAA Compliance and Enforcement — 14 CFR Part 13
2. FAA Order 2150.3C — Compliance and Enforcement Program
3. Part 135 Air Taxi & Commercial Operators — FAA
4. AOPA Legal Services Plan — Coverage Overview
5. FAA Enforcement Process — Pilot Legal Questions