Please visit https://rotate.aero/forum/relays-general/315-leach-relay-p-n-bacr13cf2a#565 for a discussion of this part number relay.

Leach relays are used extensively on all Boeing, Airbus, Douglas, and Gulfstream aircraft. They can be found in numerous other types of corporate aircraft.

They are extremely reliable as they can last numerous decades with thousands of cycles.

Years ago, I encountered a relay from a Gulfstream that was acting like the car blinkers of old. The coil would get hot and go open which caused the relay to relax. As soon as the coil cooled, it would energize again.

https://rotate.aero/forum/relays-general/79-leach-relay-coil-opens-and-closes-from-heat

In my short few months on the 767 I have found "two" examples of the same fault.

https://rotate.aero/forum/ata24-767/314-ata-24-33-stby-power-failure-indication#564

https://rotate.aero/forum/767-ata27/304-ata-27-62-auto-speedbrakes

Both have had the same part number BACR13CF2A.

In defense of Leach, both of the recently failed relays were quite old (as noted by the pitted "feel" of the case).

Aircraft had a Standby Power "OFF" light flashing intermittently on the overhead panel. Along with the light, a EICAS message of "Standby Bus Off" cycling on and off.

767's use two relays for standby power failure indication. K110 senses DC power and K138 is used for AC power. As long as power is present at each relay, they remain energized. If either power fails, the relaxed relay supplies a ground signal to both the light and EICAS systems.

Both relays are located in the forward most section of the P6 panel in the lower right section of the cockpit. (I've found that using a bungee cord to hold these types of panels open is a great help. If the aircraft is powered up, everything is hot, including the breakers on the fold out section itself. the further away from my hands..... the better.)


K110 and K138 are mounted next to each other. A clear "click" was heard every 10 seconds or so. I pulled K138 first, the sound remained. K110 was the culprit. The coil would go open when it got hot. It would close after it cooled.




767-300 ASM 24-33-01

As far as the troubleshooting on the "SPD" flag, some items need to be noted.

1. The flag did not disappear when the ADC system was switched to "Both on Two".

2. It did not show up on the F/O's side when switched to "Both on One".

3. The flag showed on F/O's side when Air/Ground system 2 was placed in air mode.

It has to be assumed that the EADI's speed indication is "on-side" only. It must take actual ram airspeed applied to indicate in the air.
Questions remain if either of those two statements are correct?????

First called out for a flagged "SPD" on the captains EADI. The speed tape should be displayed on normal system power up and it does not need the IRS's up. The on-side airspeed indicator was not flagged.



Noticed TAT(Total Air Temp) indication on EICAS reading 70C or more. Captain's pitot heat system was also indicating on.



EICAS status showed a Nose Air/Ground disagree.



The nose position disagree could be cleared via the maintenance panel reset, but we still had something stuck in air mode. Checking the Proximity Box for both nose and main gear tilt showed S246 (Right Gear - System 1) with a target showing "near" when the other three showing "far". Far is normal for ground indication.

A pitot system can be checked for leaks by just applying pressure (simulating airspeed) to the line. If the system is tight, it should hold.

My problem over the years is not having the correct pitot tube adapter and having leaks at the rubber tube placed on the probe. It's kinda tough to verify a leak if you're inducing one of your own.

I haven't checked the Boeing's, but I do know the MD-11 has sensors right at the pitot probes and static ports. The sensors send data directly to the ADIRU's. There is no need for pitot/static lines which pretty much negates the possibilities of leaks.

I'll have to look to see how 75's and 76's are connected.

Wow, I have often wondered about this problem and how to attack it on a turn. It sounds simple, since pitot pressure doesn't have an input to Altimeter reading, don't need to block off pitot probes! I like this approach Mark!!

Someone forgot to turn off BATT switch? Nice find!

Always thought it was inside the tank, wow thanks Mark!