77-25-05 ENSTROM: Amendment 39-3096. Applies to F28C and 280C helicopters certificated in all categories. Compliance required as indicated.
(a) Prior to further flight, perform Enstrom Service Information Letter No. 0069 as required to provide a smooth running idle characteristic. Adjust the idle mixture in accordance with Enstrom Service Information Letter No. 0069 steps 4C thru 4G. With the idle mixture properly adjusted perform the following check: Turn the boost on and off. Any noticeable change in RPM is an indication of internal injector leakage. If this condition is observed remove the injector and return the injector to an authorized Bendix repair station. Replace with an airworthy injector and repeat the above check.
(b) Prior to further flight incorporate the attached supplemental information in the appropriate RFM. Affix the placard as indicated and operate in accordance therewith.
(c) Within the next three calendar months or 100 hours time in service, whichever occurs first, install Enstrom Kit 28-121015.
The following limitations and procedures are effective immediately for all Enstrom Model F28C and 280C helicopters. Applicable rotorcraft flight manual pages are attached. NOTE: Compliance with the revised procedures outlined herein does not require a logbook entry. Flight manuals affected:
F-28C (December 8, 1975; revised 12/21/76)
280C (December 8, 1975; revised 12/21/76)
280C (September 23, 1977, Report No. 28-AC-016)
FLIGHT MANUAL INSERTION:
LIMITATIONS:
(To be added to all three FM's)
FUEL MIXTURE SETTING: (Page FM-2-4) In addition to present RFM procedures add:
Mixture must be leaned to at least 130 PPH at 36.5 in. MAP for all flight conditions except hover. If richer mixture required to maintain E.G.T. levels below 1650 degrees F practice autorotations are prohibited.
PLACARDS: (Page FM-2-7)
Add placard in view of pilot.
"Lean to 130 PPH at 36.5 in. MAP in flight - see revised RFM"
NORMAL PROCEDURES:
F-28C normal engine starting procedure (Page FM-3-1). Add step 22 below.
280C engine starting procedures, hot condition (Page FM-3-2). Add step 14 below.
280C hot engine restarting procedure (Page FM-3-3, Report No. 28-AC-016). Add step 15 below.
Note engine idle RPM (with boost off) and turn fuel boost on. Any difference in RPM noted indicates leaky idle mixture plates (refer to Enstrom Service Letter No. 0069). Slowly lean engine with mixture control short of cutoff position. An increase of 50 RPM indicates idle mixture improperly set (refer to Enstrom Service Letter No. 0069).
F-28C and 280C engine warm-up and ground check (Page FM-3-3). Change step 3 to below (no change required in Report No. 28-AC-016).
3. Check the magnetos using the following procedure:
A) At flat collective pitch and 2900 RPM allow the E.G.T. to stabilize, with mixture in full rich position.
B) Set the E.G.T. gauge cursor red needle to the stabilized indicated temperature. (This will be a reference temperature during the mag test.)
C) Switch from both mags position to left mag position and note RPM drop and E.G.T. rise for five seconds. The maximum allowable RPM drop is 125 RPM. The maximum allowable E.G.T. rise is 100 degrees F.
D) Return magneto switch to both allowing E.G.T. and RPM to stabilize and repeat check on the right mag position.
E) The maximum permissible RPM differential between left and right magnetos is 50 RPM without engine roughness. A differential of greater than 50 RPM and or a drop in RPM greater than 125 RPM could indicate spark plug, spark plug lead wire, or magneto problems.
F) An E.G.T. rise over 100 degrees F during operation on individual magneto indicates a magneto timing problem.
F28C and 280C flight information (Page FM-3-4). Add special instructions below.
SPECIAL INSTRUCTIONS FOR MIXTURE LEANING IN FLIGHT:
A) The mixture mustbe leaned to at least 130 PPH at 36.5 in. MAP. Do not exceed 1650 degrees F E.G.T.
B) If mixture greater than 130 PPH is required to prevent exceeding E.G.T. of 1650 degrees F, practice autorotation/power chop are prohibited.
C) With mixture leaned as prescribed in A) above, practice autorotations/power reductions are to be performed as follows;
1. Close throttle smoothly all the way to the closed position and hold on the stop, or:
2. Smoothly split needles and maintain engine RPM at 2000 or above.
3. Do not try to maintain throttle at intermediate positions between fully closed and 2000 engine RPM as this may cause inadvertent engine stoppage due to improper idle/mixture settings or faulty fuel servo.
F28C and 280C engine cooling and shutdown procedure (FM-3-5) add:
5A. Note engine idle RPM (with boost off) and turn fuel boost on. Any difference in engine RPM noted indicates leaky idle mixture plates (refer to Enstrom Service Letter No. 0069). Slowly lean engine with mixture control short of cutoff position. An increase of 50 RPM indicates the idle mixture is improperly set (refer to Enstrom Service Letter No. 0069).
The manufacturer's specifications and procedures identified in this directive are incorporated herein and made part hereof pursuant to 5 U.S.C. 552(a)(1). All persons affected by the directive who have not already received these documents from the manufacturer, may obtain copies upon request to Enstrom Helicopter Corporation, Menominee County Airport, P.O. Box 277, Menominee, Michigan 49858. These documents may also be examined at the Great Lakes Regional Office, 2300 East Devon Avenue, Des Plaines, Illinois 60018, and at FAA Headquarters, 800 Independence Avenue, S.W., Washington, D.C. 20591. A historical file on this airworthiness directive which includes incorporated material in full is maintained by the FAA at its headquarters in Washington, D.C., and the Great Lakes Region.
This supersedesthe AD issued by airmail letter dated September 30, 1977, as amended by airmail letter dated October 25, 1977.
This amendment becomes effective December 21, 1977, and was effective for all recipients of the airmail letter dated November 7, 1977, upon receipt thereof.