AD 52-19-01 ACTIVE

52-19-01 CURTISS-WRIGHT: Applies to all Models of C-46 Series airplanes used in passenger operation under the provisions of Parts 41, 42, and 61 of the Civil Air Regulations as specified in 41.20(f), 61.31(b), and Amendment 42-2 dated November 1, 1946.

Item (5) of this Directive must be accomplished by November 1, 1952. The other items should be accomplished as soon as possible but not later than April 1, 1953.

(This note pertains only to the powerplant fire protection aspects of the above Regulations. AD's 49-18-01 and 49-25-01 cover the fire prevention for the cabin heater installation, and for the baggage and cargo compartments of the airplane respectively.)

Recent experience with the C-46 aircraft in passenger operation has brought to light several instances in which the adequacy of the powerplant fire protection installation provided is questionable. This Directive, which cancels and supersedes AD 49-19-1, therefore is intended to correct those installations wherein such inadequacies may exist.

(1) Shutoff Valves. Install fluid shutoff valves, which may be opened and closed in flight, aft of the firewall in all fuel, oil, and hydraulic lines. USAF Technical Order 01-25LA-190 covers this same subject. If propeller or carburetor anti-icing systems are employed and use alcohol or other flammable fluids as the anti-icing medium, the systems described in USAF T.O. AN 01-25LA-2, pages 458-464, are satisfactory except that shutoff valves or a selector valve which can be opened and closed in flight must be provided aft of the firewall, to shut off the flow to either engine. The system should be such as to shut off the pump automatically, or otherwise guard against hazardous pressures, when the flow to both nacelles is stopped. (No shutoff valve will be required for the feathering pump oil lines, see section (3) below.)

(2) Engine Firewalls. Engine firewalls must be rendered fireproof by adequately sealing all openings such as the filtered air duct opening, the oil cooler control rod and filtered air control rod openings, other powerplant control openings, holes through the firewall for electric conduits, and any other firewall openings.

(3) Propeller Feathering Pump Installation. The portion of the propeller feathering oil line forward of the firewall between the firewall and the pump shall be of steel or other fireproof material. The line between the pump and governor shall be of fire resistant material with coupled hose assemblies used in any flexible connections. Electrical conduit for the pump motor and other electrical components forward of the firewall which are essential for propeller feathering shall be fire resistant or protected in a manner to render them fire resistant. The feathering pump can be considered an adequate means of shutting off the flow of oil in the feathering line.

(4) Fire Extinguisher System.

(a) Carbon Dioxide Quantity and Rate. The fire extinguisher system must be improvedto provide at least 35# carbon dioxide per shot which must be discharged into the nacelle at a rate of not less than 17 1/2#/sec (the rate of discharge will be affected by the number of bottles, the discharge valve sizes, the line sizes, and the nozzle area). The portion of the two- shot fire extinguisher system which is described in USAF Technical Order 01-25LA-205 is satisfactory. (Note: Civil Aeronautics Board Draft Release No. 52-15, proposes to require a two- shot fire extinguisher system in these airplanes in the near future. Operators, therefore, may consider it more practical to accomplish both changes at the same time.

(b) Distribution System. The piping and nozzle arrangements shall be such as to spray the bulk of the discharge in the power section with a smaller amount (approximately 7 percent) being sprayed over the oil cooler. In this regard, it will be acceptable, if desired, to split the power section portion of the discharge so as to spray approximately one-thirdof it from 5 nozzles located around the upper half of the engine mounting ring.

(c) Nozzle Location and Spray Pattern. The location of the nozzles and pattern of their spray are important for effective fire extinguishing and shall be substantially as follows:

1. For the power section, a nozzle shall be located at the rear and the base of each cylinder, discharging the carbon dioxide in a fan spray radially away from the crankcase. The provisions of USAF Technical Order 01-25LA-162 pertaining to replacement of engine cylinder fire extinguisher nozzle brackets must be accomplished.

2. For the oil cooler, a nozzle or nozzles shall be located above the forward end of the cooler directing fan sprays down and forward on each side of the cooler and duct.

3. The five nozzles located around the upper half of the mounting ring, if used, shall be such as to direct a fan spray radially outward as well as a fan spray radially inward over the accessories.

(5) Fire Detectors. The Fenwal continuous type fire detectors, which were originally provided must be removed and replaced with unit or continuous type fire detectors conforming with FAA Technical Standard Order, TSO-C11 or TSO-C11a. If unit type detectors are used, they shall be spaced as specified below. Continuous type detectors, if used, shall be so installed as to provide equivalent coverage.

(a) Engine Nacelles. Fire detectors, spaced not over 7 inches apart, shall be installed on the lower half of the forward side of the firewall at its outer periphery, and along the horizontal diameter.

(b) Engine Mount Ring and Oil Cooler Supports. Additional fire detectors, spaced not over 18 inches apart, shall be provided for the upper two-thirds of the engine mount ring. Also, a fire detector shall be installed on each oil cooler support approximately 2 to 3 inches above the oil cooler.

(c) Warning Light Covers. Fire-warning-light covers or shutters which are capable of dimming or shutting off the light entirely, must be removed.

(6) Engine Compartment Lines. The following lines carrying inflammable fluids or vapors in the engine compartment shall be fire resistant and items (a) through (g) inclusive shall also have fireproof firewall fittings. Flexible connections in lines attached to the engine or subject to relative motion or pressure shall employ fire resistant coupled hose assemblies: (a) carburetor bleed back lines, (b) cabin heater fuel lines, (c) oil dilution lines, (d) fuel pressure transmitter lines, (e) oil pressure transmitter lines, (f) manifold pressure lines, (g) all other hydraulic oil lines, (h) all engine fuel lines, (i) engine primer lines, (j) engine breather lines, (k) engine supercharger drain lines, (l) oil separator return lines, (m) vacuum system pressure lines, (n) all main oil lines, (o) engine oil cooler lines, (p) hydraulic pump drain lines, (q) exhaust collector drain lines, (r) oil tank vent lines, (s) fuel pump drainlines.

The fire extinguisher distribution tubing and fittings ahead of the firewall must be of steel or other fireproof material. Flexible connections in the distribution tubing ahead of the firewall must be at least of fire resistant construction, and shall use coupled hose assemblies rather than hose clamp connections.

(7) Airplane Flight Manual. Appropriate changes to the airplane flight manual shall be prepared to cover emergency procedures associated with the above changes.

(8) More detailed information on methods of complying with this Directive is being furnished to CAA Agents.