AD 91-21-07
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | The Boeing Company | DC-9-11 | Airworthiness Directives; MCDONNELL DOUGLAS DC-9 and DC-9-80 Series Airplanes, Model MD-88 Airplanes, and C-9 (Military) Airplanes |
| aircraft | The Boeing Company | DC-9-12 | Airworthiness Directives; MCDONNELL DOUGLAS DC-9 and DC-9-80 Series Airplanes, Model MD-88 Airplanes, and C-9 (Military) Airplanes |
| aircraft | The Boeing Company | DC-9-13 | Airworthiness Directives; MCDONNELL DOUGLAS DC-9 and DC-9-80 Series Airplanes, Model MD-88 Airplanes, and C-9 (Military) Airplanes |
| aircraft | The Boeing Company | DC-9-14 | Airworthiness Directives; MCDONNELL DOUGLAS DC-9 and DC-9-80 Series Airplanes, Model MD-88 Airplanes, and C-9 (Military) Airplanes |
| aircraft | The Boeing Company | DC-9-15 | Airworthiness Directives; MCDONNELL DOUGLAS DC-9 and DC-9-80 Series Airplanes, Model MD-88 Airplanes, and C-9 (Military) Airplanes |
| aircraft | The Boeing Company | DC-9-15F | Airworthiness Directives; MCDONNELL DOUGLAS DC-9 and DC-9-80 Series Airplanes, Model MD-88 Airplanes, and C-9 (Military) Airplanes |
| aircraft | The Boeing Company | DC-9-21 | Airworthiness Directives; MCDONNELL DOUGLAS DC-9 and DC-9-80 Series Airplanes, Model MD-88 Airplanes, and C-9 (Military) Airplanes |
| aircraft | The Boeing Company | DC-9-31 | Airworthiness Directives; MCDONNELL DOUGLAS DC-9 and DC-9-80 Series Airplanes, Model MD-88 Airplanes, and C-9 (Military) Airplanes |
| aircraft | The Boeing Company | DC-9-32 | Airworthiness Directives; MCDONNELL DOUGLAS DC-9 and DC-9-80 Series Airplanes, Model MD-88 Airplanes, and C-9 (Military) Airplanes |
| aircraft | The Boeing Company | DC-9-32 (VC-9C) | Airworthiness Directives; MCDONNELL DOUGLAS DC-9 and DC-9-80 Series Airplanes, Model MD-88 Airplanes, and C-9 (Military) Airplanes |
Unsafe Condition
Overheating of primary longitudinal trim relays (P/N 9207-8333, -8333-1, -8968, -10101, -10296, -10166) could lead to fire in the forward cargo compartment due to contact degradation, arcing, or carbon build-up.
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Required Actions
Inspect relays for contact degradation, arcing, carbon build-up, or abnormal wear; perform functional checks per service bulletin. Replace relays with new approved parts at specified intervals (8,000 or 16,000 flight hours depending on model).
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Compliance Time
Within 17 or 30 days after February 27, 1991, or prior to 8,000 or 16,000 flight hours on the relays, whichever is later. Subsequent replacements every 8,000 or 16,000 flight hours.
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Affected Aircraft
McDonnell Douglas DC-9 and DC-9-80 series airplanes, Model MD-88, and C-9 (Military) airplanes equipped with Primary Longitudinal Trim Relays (P/N 9207-8333, -8333-1, -8968, -10101, -10296, -10166).
AI-generated summary from the source AD text. Verify against the official source before acting.
Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
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