|Object Type:||Signal/Data Processor|
|Object Name:||Interlock Failure Monitor|
|Division:||Flight Controls [FCD]|
|Platform(s):||BAC 1-11 , Concorde , VC10|
|Year of Manufacture:||circa 1970|
|Location:||Rack RAA01 [Main Store]|
Interlock Failure Monitor
Type No. 8383-A-1
Ser No. 048/70
BAC 1-11 Aircraft Only
Beware Static Damage
MA Service & Repair Division
GAv(R) A.S.&R.D. 86
The Interlock Failure Monitor does not appear on the system description of the BAC 1-11 2000 AFCS although the box is ‘BAC 1-11 AIRCRAFT ONLY’. The unit is described in the literature for the VC10 AFCS so was used in both systems.
In 1964 Elliott Bros designed an ‘Interlock Monitor’ system to locate which element of the automatic landing system had failed in the event of an interlock opening and causing autopilot disconnect. In those days, autopilot engagement was permitted when a discrete number of series relay contacts had been closed by the discrete monitor circuits the nature of the design was that, if one relay opened, there would be subsequent operation of the other relays due to the fail-safe method of combining the fault detecting relay contacts.
The equipment added to the automatic landing system was basically an on-aircraft fault diagnosis. It comprised a small digital computer and a simple multi-lamp display panel and reset switch. The Interlock Monitor Computer scanned the series of relay interlocks and detected which one opened first. This therefore located the failure to the particular comparator, identified by a corresponding lamp number on the display panel.
The equipment was first used in 1965 and became standard equipment for BOAC. Considerable problems were encountered due to the large number of interlocks which were in use over long periods in flight. The Monitor was eventually able to discriminate faults to an acceptable level of non-ambiguity only after considerable refinement of the in-line monitoring design.
There are two patch-boards under hinged covers either side of the unit’s handle. The left-hand panel has sockets 1-18 and the right-hand panel 19-36. Both sides have a shorting-pins stowed inside the cover. Presumably these pins short two layers of contacts beneath each of the numbered holes; possibly the hidden layer is common to them all, allowing point A to be connected to point B just by putting pins in A & B holes. At present we have not discovered how these pins were used.
This system was applied to the VC10, the super BAC 1-11 and Concorde.