# AD 72-20-03: Heater Overheat

- Type: Airworthiness directive
- Status: Current
- Products: Textron 65-90, 65-A90, 99, 99A, A99A, B90 and B99
- Effective: September 27, 1972
- Superseded by: Nothing supersedes this AD
- Product type: Aircraft, Small airplane
- Amendment: 39-1524
- Registered aircraft: 110 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/6AA0320DC1C9183586256A08007389B5.0001
- DRS record last changed: January 21, 2026
- Page: https://openairdocs.org/ad/72-20-03

## The airworthiness directive

72-20-03 BEECH: Amendment 39-1524. Applies to Models 65-90, 65-A90 and B90 (Serial Numbers LJ-1 thru LJ-501) airplanes and to Models 99, 99A, A99A and B99 (Serial Numbers U-1 thru U-151) airplanes.

Compliance: Required as indicated, unless already accomplished.

To prevent heater overheat which melts the windshield defroster ducting, damages wiring beneath the instrument panel and fills the cabin with smoke, accomplish the following:

A) Effective immediately, operation of the heater is prohibited if the ventilation blower is not functioning.

B) Prior to each flight determine that the ventilation blower is operating.

NOTE: This determination may be made by checking for air flow out of the air distribution openings in the cockpit and/or by the sound of the blower.

C) Within 25 hours' time in service after the effective date of this AD:

  (1) Remove and replace existing vent blower and combustion differential switches with Beech P/N 90-380010-1 differential pressure switches in accordance with Beechcraft Service Instructions No. 0500-412 or later revision.

  (2) Inspect the heater fuse to determine that a standard fuse of proper value is installed and if an improper fuse is found, prior to further flight, install standard fuse of proper value.

NOTE: Beechcraft Service Instructions No. 0500-412 or later revision lists proper fuses.

D) When Paragraph C has been complied with the limitation in Paragraph A may be removed and the check required by Paragraph B may be discontinued.

E) Any equivalent method of compliance with this AD must be submitted to and approved by the Chief, Engineering and Manufacturing Branch, FAA, Central Region.

This amendment becomes effective September 27, 1972.

## Affected data sheets (2) (OpenAirDocs)

The type certificate data sheets whose models the AD names.

- [TCDS A14CE](https://openairdocs.org/tcds/A14CE): Textron Aviation Inc.; names 4 of 12 models: A99A, B99, 99A, 99
- [TCDS 3A20](https://openairdocs.org/tcds/3A20): Textron Aviation Inc.; names 3 of 22 models: B90, 65-A90, 65-90

## Registered aircraft it may apply to (OpenAirDocs)

Matched by airframe and engine model; the AD's applicability may narrow it by serial number, part number or equipment.

- Aircraft: 110 (110 by airframe model, 0 by engine model)
- Makers: Beech 110

Models with the most aircraft:

- [Beech 65-A90](https://openairdocs.org/model/beech-65-a90): 34 aircraft (airframe model)
- [Beech B90](https://openairdocs.org/model/beech-b90): 29 aircraft (airframe model)
- [Beech 99](https://openairdocs.org/model/beech-99): 23 aircraft (airframe model)
- [Beech 99A](https://openairdocs.org/model/beech-99a): 11 aircraft (airframe model)
- [Beech 65-90](https://openairdocs.org/model/beech-65-90): 7 aircraft (airframe model)
- [Beech B-99](https://openairdocs.org/model/beech-b-99): 6 aircraft (airframe model)

All 6 models: https://openairdocs.org/ad/72-20-03/models.md
Every aircraft: https://openairdocs.org/ad/72-20-03/aircraft.md

Its text cites no advisory circulars or STCs.

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