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VFR REGULATIONS 17 / LEARN · EXPLORE · CHECK

Transponder requirements

The veil and the shelf are different boundaries.

Checking your account…

Your learning goals

  • Apply where the usual trainer needs it.
  • Recognize the limits and exceptions that affect this flight.
  • Explain a decision using the scenario and supporting rule.

Where the usual trainer needs it

  • Class B and C (and Class A, outside ordinary VFR operations).
  • Within the 30-NM veil of an Appendix D section 1 airport, surface to 10,000 MSL.
  • Above a B/C ceiling within its lateral boundaries, up to 10,000 MSL.
  • In the contiguous 48 states/DC, at or above 10,000 MSL, except airspace at or below 2,500 AGL.

The usual requirement includes a coded transponder and automatic pressure-altitude reporting. Consult the rule’s additional designated-airport provision where applicable. Being under a B shelf does not put you outside its 30-NM veil.

14 CFR §91.215

Equipment and operation are separate

An operable, properly maintained transponder must normally be operated, including altitude reporting if installed, in required airspace and all controlled airspace unless ATC directs otherwise under the rule. A portable traffic display is not a transponder.

14 CFR §91.215

Exceptions need an actual basis

Specific provisions exist for aircraft not certificated with an engine-driven electrical system, and balloons/gliders; limits differ by airspace. A failed alternator does not create that exception. Unequipped-aircraft deviation requests generally need at least one hour’s notice; approval is not guaranteed. Broken equipment has a different request provision.

14 CFR §91.215

FLIGHT SCENARIO

What would change your plan?

You stay below the Class B shelf but remain 20 NM from a listed primary airport. Does that avoid the Mode C veil?

  1. NoticeWhat does this situation require?
  2. VerifyWhat evidence is still missing?
  3. DecideWhat keeps an option open?
Compare your reasoning

No. The 30-NM veil is separate from the shape of Class B. Check equipment or a genuinely applicable exception/authorization.

SUMMARY

The veil and the shelf are different boundaries.

No. The 30-NM veil is separate from the shape of Class B. Check equipment or a genuinely applicable exception/authorization.

Before moving on, explain the decision in your own words: what would you verify, and what would make you change the plan?

PRACTICE

Flashcards and knowledge check

Six flashcards, then five questions with explanations.

Enable JavaScript for flashcards and the knowledge check. The lesson and scenario remain available without it.

Sources & lesson notes

Sources & lesson notes

  1. 14 CFR §91.215Verified against eCFR text current through September 15, 2026.

For U.S. private-pilot airplane study. Rules verified against eCFR text current through September 15, 2026, with linked FAA guidance. Scenarios isolate a rule; actual flight decisions require all applicable rules, aircraft limitations, and current information.