Technically: Service Bulletin 21-4165: Air Conditioning – Duct Plug Inspection

Technically: Service Bulletin 21-4165: Air Conditioning – Duct Plug Inspection

TechIssued: August 2016

Compliance – Recommended: This Service Bulletin should be accomplished at a scheduled maintenance period or inspection.

NOTE: This Service Bulletin may be completed at a time when Left and Right Passenger Compartment Cabin Window Panels are removed to facilitate other maintenance such as at the first Cross Tie Inspection at 2500 cycles.

A service bulletin published by Textron Aviation may be recorded as completed in an aircraft log only when the following requirements are satisfied:

  1. The mechanic must complete all of the instructions in the service bulletin, including the intent therein.
  2. The mechanic must correctly use and install all applicable parts supplied with the service bulletin kit. Only with written authorization from Textron Aviation can substitute parts or rebuilt parts be used to replace new parts.
  3. The mechanic or airplane owner must use the technical data in the service bulletin only as approved and published.
  4. The mechanic or airplane owner must apply the information in the service bulletin only to aircraft serial numbers identified in the Effectivity section of the bulletin.
  5. The mechanic or airplane owner must use maintenance practices that are identified as acceptable standard practices in the aviation industry and governmental regulations.

No individual or corporate organization other than Textron Aviation is authorized to make or apply any changes to a Textron Aviation-issued service bulletin, service letter, or flight manual supplement without prior written consent from Textron Aviation.

Textron Aviation is not responsible for the quality of maintenance performed to comply with this document, unless the maintenance is accomplished at a Textron Aviation-owned Service Center.

Effectivity: Beechcraft Super King Air B300/B300C Fusion, Serial Numbers FL-1032 through FL-1041, FL-1043, FL-1049, FL-1053 through FL-1055 and FL-1057.

The equivalent of this Service Bulletin has been incorporated on production airplanes FL-1058 and on.

Reason: This Service Bulletin is being issued to inspect for missing distribution duct plugs to ensure installation meets type design and to ensure adequate air flow distribution.

Description: This Service Bulletin provides parts and instructions to inspect for and if necessary install
300-1184-1 upper duct plugs at FS 156.00.

Warranty: Eligible airplanes may qualify for parts and labor coverage to the extent noted in the Labor Hours and Material Availability sections of this document. (Editor’s Note: Full service bulletin can be found on company website).

From King Air Communiqué 2016-08:

Issued: July 2016

ATA 30 – Prop Heat Operational Check Procedure – Engines Not Running

BY-122, BY-124 and after; BZ-1 and after

King Air Communiqué 2015-07 was issued to remind owner/operators not to operate the propeller heat when the engines are not running. This action helps to prevent damage to the propeller blades and de-ice boot. The propeller manufacturer has also placed a 10-second limitation on operating the propeller heat with the engines not running. This limit creates an issue when performing a propeller heat test because the timer in the propeller de-ice system cycles the power to the left and right propeller every 90 seconds. This condition makes it impossible to assure that the propeller heat system is operating correctly while the airplane is in the hangar. The system can still be tested during ground runs with the engines running. The following paragraph provides a procedure that tests the system without applying power to the boots.

Propeller De-ice Boot Continuity Check: Check the resistance of each de-ice boot by disconnecting the boot and testing it individually. Continuity through the slip rings can be measured with the boots connected by disconnecting the brush block and measuring the resistance between the rings. Resistance will vary by how many boots are connected. Verify that there is good continuity. Resistance can also be measured between the two terminals on the brush block assembly with the wires disconnected. Remember that the resistance will vary.

Refer to the following chart for the resistance values.

Temperature Range °F

Temperature Range °C

1 Boot

Min Ohms

Max Ohms

0 to 5

-17.8 to -15.0



5 to 10

-15.0 to -12.2



10 to 15

-12.2 to -9.4



15 to 20

-9.4 to -6.7



20 to 25

-6.7 to -3.9



25 to 30

-3.9 to -1.1



30 to 35

-1.1 to 1.7



35 to 40

1.7 to 4.4



40 to 45

4.4 to 7.2



45 to 50

7.2 to 10.0



50 to 55

10.0 to 12.8



55 to 60

12.8 to 15.6



60 to 65

15.6 to 18.3



65 to 70

18.3 to 21.1



70 to 75

21.1 to 23.9



75 to 80

23.9 to 26.7



80 to 85

26.7 to 29.4



85 to 90

29.4 to 32.2



90 to 95

32.2 to 35.0



95 to 100

35.0 to 37.8



Note: Ambient air temperature may not represent the de-ice boot temperature. Solar or infrared heating will affect the temperature of the de-ice boot.

De-ice timer check: Connect a 28 VDC lamp to terminal block E21 on the left and right engine. Turn power ON and place the De-Ice switch to AUTO position. The light should illuminate and alternate between the left and right engine approximately every 90 seconds.

ATA 33 – Emergency Exit Sign Bulb Replacement and Alternate Part Number

B300 Series

The FWD and AFT Emergency Exit signs located in the headliner of the Model B300 Super King Air airplane come from the factory with an incandescent lamp, DS1, which can be prone to loosening in its socket due to vibration or burning out. Textron Aviation has approved an LED replacement for this lamp with Part Number E10-WHP. When the lamp is replaced, either with the incandescent or LED Light, Textron Aviation recommends the use of F900 torque seal on one side of the socket to lamp base. This approved material is listed in Chapter 20 Consumable Materials for King Air Models and may be used to secure the lamp in the socket.   

ATA 46 – XM Weather TAF Data on Pro Line 21 King Airs with XM Receiver
Part Number 822-2031-002 

Beginning in early 2016, Rockwell Collins began receiving reports of intermittent reception of Terminal Area Forecast (TAF) data through the XM weather receiver installed in Pro Line 21 airplanes. This data includes products such as METARs and AIRMETs. Investigation determined that the National Weather Service had increased the data package size of these messages and the current configuration of the receiver was causing a software time-out and reset before the complete data package was downloaded.

Any owner/operators experiencing this issue may utilize Rockwell Collins Service Information Letter (SIL) 523-0824074 (Editor’s Note: See SIL online with this Communiqué) to provide an updated receiver configuration that allows it to handle the new data package size. Airplanes with factory installed Fusion avionics are not affected. Pro Line 21 airplanes that have been upgraded to Fusion avionics through an STC may still have the Part Number 822-2031002 receiver and require the update. Refer to Appendix A.

ATA 54 – Nacelle Splice Plate Inspection

A new inspection requirement has been added to the Model B300 King Air Maintenance Manual. This inspection addresses the nacelle splice plates. Even though this inspection has been in the manual set for many years for other King Air models, it is new on the King Air B300 and it will eventually be added to the King Air 200 and 300 Series Maintenance Manuals as well.

Textron Aviation Technical Support has received inquiries from B300 owner/operators asking for information about the nacelle splice plates since they are not familiar with this new requirement. The purpose of this Model Communiqué is to define the scope of the inspection, provide illustrations of where the nacelle splice plates are located, provide examples of corrosion that have been found in past inspections and explain why these inspections are now required.

A severely corroded example.
A severely corroded example.

The nacelle splice plates are located under the nacelle turtle back. There are two per side and they run longitudinal. (Editor’s Note: illustrations provided with Communiqué on website.) For airplanes without wing lockers, the turtle back should to be removed. As an alternative, the nacelle splice plate edge may be inspected through the main landing gear wheel well. For airplanes with wing lockers, the splice plates are exposed when the lockers are removed. Model 350ER airplanes will have to deal with external fuel tanks, but the intent of the inspection is met by inspecting the edge of the part as seen through the main landing gear wheel well area. This inspection procedure is in­cluded in the SIRM for other King Air models and can be used as a reference until the SIRM is updated to include this procedure in the B300 section.

The above information is abbreviated for space purposes. For the entire communication, go to

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