# AD 75-26-07: Electrical Fire Hazards

- Type: Airworthiness directive
- Status: Current
- Products: Viking Air DHC-6-1, DHC-6-100, DHC-6-200 and DHC-6-300
- Effective: December 17, 1975
- Superseded by: Nothing supersedes this AD
- Product type: Aircraft, Small airplane
- Amendment: 39-2455
- Registered aircraft: 88 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/223298AAEEC9699486256A3800493230.0001
- DRS record last changed: May 30, 2024
- Page: https://openairdocs.org/ad/75-26-07

## The airworthiness directive

75-26-07 De Havilland: Amendment 39-2455. Applies to all DeHavilland Model DHC-6 Series Twin Otter aircraft certificated in all categories.

Compliance required as indicated to preclude the hazards of an electrical fire due to contact welding of the reverse current relay(s), Hartman part number A700AP or A700AAP.

1. For aircraft containing reverse current relays which have between 1000 to 2400 hours time in service since new or overhauled, or aircraft having reverse current relays which have less than 1000 hours time in service which have been used for cross generator engine starts, accomplish the following:

      (A) Within the next 25 hours time in service, after the effective date of this AD, unless already accomplished,

    (i) Remove the reverse current relays from the aircraft.

    (ii) Examine relay for indications of overheat.

    (iii) Inspect relay contact points under ten-power glass for signs of pitting, corrosion or other surface damage.

If anyof the above conditions in 1(A) (ii) or 1(A) (iii) are present, replace relay with a serviceable unit before further flight.

2. This applies to aircraft containing reverse current relays with more than 2400 hours' time in service since new or overhauled.

      (A) Unless already accomplished, inspect relays in accordance with Paragraph 1(A) of this AD

      (B) Unless accomplished, within the previous 2400 hours' time in service after the effective date of this AD, conduct bench tests of reverse current relays within the next 100 hours' time in service after the effective date of this AD, in accordance with DeHavilland of Canada LTD. PSM 1-6-2 Part 7 or PSM 1-63-2 Chapter 24-30-00.

3. Within the next 10 flight hours, install the following placard in full view of the pilot:

"CROSS GENERATOR ENGINE STARTING IS PROHIBITED, EXCEPT IN AN EMERGENCY."

4. Following a flight for which an emergency cross generator engine start was made, within the next 25 hours' time in service, accomplish the inspection required by paragraph 1(A) of this AD.

5. If any inspection required by this AD is not accomplished within specified time above, airplane may be flown in accordance with FAR 21.197 to a base where inspections can be made.

This amendment is effective December 17, 1975.

## Affected data sheets (1) (OpenAirDocs)

The type certificate data sheets whose models the AD names.

- [TCDS A9EA](https://openairdocs.org/tcds/A9EA): De Havilland Aircraft of Canada Limited; names 4 of 5 models: DHC-6-1, DHC-6-100, DHC-6-200, DHC-6-300

## 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: 88 (88 by airframe model, 0 by engine model)
- Makers: Dehavilland 84, Dehavilland Acft Of Canada 4

Models with the most aircraft:

- [Dehavilland DHC-6-300](https://openairdocs.org/model/dehavilland-dhc-6-300): 59 aircraft (airframe model)
- [Dehavilland DHC-6-200](https://openairdocs.org/model/dehavilland-dhc-6-200): 19 aircraft (airframe model)
- [Dehavilland DHC-6-100](https://openairdocs.org/model/dehavilland-dhc-6-100): 6 aircraft (airframe model)
- [Dehavilland Acft Of Canada DHC 6-300](https://openairdocs.org/model/dehavilland-acft-of-canada-dhc-6-300): 4 aircraft (airframe model)

All 4 models: https://openairdocs.org/ad/75-26-07/models.md
Every aircraft: https://openairdocs.org/ad/75-26-07/aircraft.md

Its text cites no advisory circulars or STCs.

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