# AD 78-21-05: Tail Rotor Blades

- Type: Airworthiness directive
- Status: Current
- Products: Sikorsky S-58BT, S-58DT, S-58ET, S-58FT, S-58HT and S-58JT
- Effective: November 30, 1978
- Superseded by: Nothing supersedes this AD
- Product type: Aircraft, Rotorcraft
- Amendment: 39-3322
- Registered aircraft: 10 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/E40FE7342F0A111886256A56004B282B.0001
- DRS record last changed: May 30, 2024
- Page: https://openairdocs.org/ad/78-21-05

## The airworthiness directive

78-21-05 SIKORSKY AIRCRAFT: Amendment 39-3322. Applies to S-58BT, S-58DT, S-58ET, S-58FT, S-58HT, and S-58JT helicopters certificated in all categories.

To prevent possible tail rotor instability accomplish the following:

Within 200 hours time in service or three months, whichever comes first, after the effective date of this AD, unless already accomplished, complete the following:

  (a) Install improved abrasion strips, Sikorsky Modification Kit 58070-10008-011, on tail rotor blades, P/Ns S1615-30100-3, -4, -7, -10, -11, -15, -16, -041, -042, and -043. This modification is covered by Sikorsky Service Bulletin No. 58B15-18.

  (b) Install Sikorsky control rod assembly, P/N 58400-64010-101.

This modification is covered by Sikorsky Service Bulletin No. 58B40-5.

This amendment becomes effective November 30, 1978.

## Affected data sheets (1) (OpenAirDocs)

The type certificate data sheets whose models the AD names.

- [TCDS 1H11](https://openairdocs.org/tcds/1H11): Centerpointe Aerospace Inc.; names 6 of 15 models: S-58FT, S-58HT, S-58ET, S-58DT, S-58BT, S-58JT

## 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: 10 (10 by airframe model, 0 by engine model)
- Makers: Sikorsky 10

Models with the most aircraft:

- [Sikorsky S-58JT](https://openairdocs.org/model/sikorsky-s-58jt): 5 aircraft (airframe model)
- [Sikorsky S-58ET](https://openairdocs.org/model/sikorsky-s-58et): 3 aircraft (airframe model)
- [Sikorsky S-58BT](https://openairdocs.org/model/sikorsky-s-58bt): 1 aircraft (airframe model)
- [Sikorsky S-58DT](https://openairdocs.org/model/sikorsky-s-58dt): 1 aircraft (airframe model)

All 4 models: https://openairdocs.org/ad/78-21-05/models.md
Every aircraft: https://openairdocs.org/ad/78-21-05/aircraft.md

Its text cites no advisory circulars or STCs.

## NTSB investigations that cite this AD (1)

From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model.

- [NTSB ERA12LA493](https://openairdocs.org/ntsb/ERA12LA493), Aug 1, 2012: Sikorsky S-58JT (N126GW), Middletown, DE, substantial damage. Probable cause: The pilot's failure to recognize that the helicopter was experiencing tail rotor dynamic instability and to take immediate corrective actions during an external load lift, which resulted in the…

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