L-1011 Navigation: RDDMI (34-7)

A DME failure will cause a fail flag to appear in the DME window (arrow 1). A VHF failure will cause the appropriate VOR1 or VOR2 fail flag to appear (arrow 2). 

L-1011 Navigation: RDDMI (34-6)

The RDDMI's are located on the Captain and F/O's instrument panels. They display the following NAV data:

• NAV 1 DME
• NAV 2 DME
• And a combination of VOR and ADF directional information, depending on pilot selection.

The VOR and ADF source selection is made with the black switches on the bottom left and bottom right of the instrument. A flag right above the switch shows which NAV source is being displayed by which needle. 

Avionics Bending: RDDMI Pointer - Pinout

The second posting for the RDDMI deals with the pointers and the rotating compass card. Each of these elements is controlled by a synchro.

The compass card has one signal source and both the single as well as the double barbed arrow can be switched between ADF 1/VOR1 and ADF2/VOR2 respectively. Below is the pointer schematic for the RDDMI:

Below is the pinout for the RDDMI:

J1	01	Heading Input (X)
J1	02	Heading Input (Y)
J1	03	Heading Input (Z)
J1	08	Heading Synchro (X)
J1	09	Heading Synchro (Y)
J1	10	Heading Synchro Excitation
J1	11	VOR 2 Synchro (X)
J1	12	ADF 2 Excitation
J1	13	ADF 2 Synchro (X)
J1	15	ADF 1 Synchro (X)
J1	16	VOR 1 Excitation
J1	17	VOR 1 Synchro (X)
J1	18	115V 400Hz Power Input (Hi)
J1	23	Heading Synchro (Z)
J1	24	Heading Synchro Excitation Ground
J1	25	VOR 2 Synchro (Y)
J1	26	VOR 2 and ADF 2 Excitation Ground
J1	27	VOR 2 Excitation
J1	28	VOR 2 and ADF 2 Synchro (Z)
J1	29	ADF 2 Synchro (Y)
J1	30	ADF 1 Synchro (Y)
J1	31	ADF 1 and VOR 1 Synchro (Z)
J1	32	ADF 1 Excitation
J1	33	VOR 1 and ADF 1 Excitation Ground
J1	34	VOR 1 Syncrho (Y)
J1	38	VOR 2 - Flag
J1	40	ADF 2 - Flag
J1	54	ADF 1 - Flag
J1	55	VOR 1 - Flag
J2	b	DME1 Warning Flag - 28VDC
J3	b	DME2 Warning Flag - 28VDC
J3	B	DME2 - DATA
J2	B	DME1 - DATA
J3	S	DME2 - WORD SYNC
J2	S	DME1 - WORD SYNC
J2	T	DME1 - CLOCK
J3	T	DME2 - CLOCK

Avionics Bending: RDDMI Digital DME Display - Pinout

The dual DME readouts are independent from the radial displays below. There is a DME indicator for DME1 and one for DME2. Below is the schematic for the dual DME display:

Here is the pinout:

Conector J2

Pin B: DME 1 Serial Data In

Pin T: DME 1 Serial Data Clock

Pin S: DME 1 Word Sync

Pin b: DME 1 Flag

Conector J3

Pin B: DME 2 Serial Data In

Pin T: DME 2 Serial Data Clock

Pin S: DME 2 Word Sync

Pin b: DME 2 Flag

Avionics Bending: Radio Digital Distance Magnetic Indicator (RDDMI) (Analysis)

The RDDMI instrument used on the Lockheed L-1011 is a rather generic one. Many of the RDDMI units used on the L-1011 did not provide the capability to switch from VOR to ADF with the two switches to the bottom right and the bottom left of the unit.


The units I picked for my project are actually from two different aircraft. The one featured in the blog posting was flown on a Boeing 737 and the other one that I used on this project was flown on a Boeing 747. However, the same RDDMI instrument was also used on the Lockheed L-1011.

Here are the internals of the instrument:

1) Top View


2) Left side

3) Bottom view


4) Right side


The two needles on the front of the instrument are driven by two Synchro Receivers. They are arranged in a rather interesting way. The shaft of the receiver in the back runs through the synchro receiver in the front.