VC10 Comparison Air Data Sensor

Technical Information

Catalogue No: C0928
Category: Air Data
Object Type: Sensor/Transducer
Object Name: VC10 Comparison Air Data Sensor
Part No: 3D731-A-2
Serial No: 130/64
Manufacturer: Elliott Bros
Division: Unknown
Platform(s): VC10 
Year of Manufacture: 1964
Width (mm):
Height (mm):
Depth (mm):
Weight (g):
Location: Archive Object Store

Comparison Air Data Sensor
Type No. 3D731-A-2
Ref. No. V.A.A.S No. 202 (ET)
Ser. No. 130/64


The automatic flight control system of the Standard and Super VC10 was designed to be capable of development to full blind landing. To meet this requirement the system had to be capable of failure survival and this includes associated services such as power supplies and flying controls. The method of autopilot failure survival chosen was to provide two monitored systems which are fail soft, i.e. there is negligible aircraft disturbance after a failure. Only one autopilot is used to fly the aircraft, and the two systems, including power supplies, are completely independent.

Each autopilot has a comparison monitor which detects faults and, in flight, will disconnect the system if these faults are likely to lead to dangerous conditions. For autoflare the system provides for automatic changeover to the second monitored autopilot system, in the event of fault in the first. Under these conditions the second autopilot is primed and ready to take over. If for any reason the monitoring system fails to prevent an autopilot runaway, the control movement is limited to a safe amount by the yielding of a torque-limiting spring.

Many of the needed components were already present in the autopilot fit on the Standard VC10s, to achieve the autoland capacity the system on the Super received some additional items. The system, supplied by Elliott Brothers (London) Ltd, is based largely on components of the well-proved Bendix PB-20 autopilot, made under licence by Elliott, and interchangeable with American built components as installed in Boeing 707s. However, the system as a whole i.e., the dual autopilot concept was novel, and designed entirely by Elliott.

In the Air Data Sensor static and dynamic pressure are sensed and three components are derived. The main outputs from the Air Data Sensor are duplicated but the outputs of the actual sensing capsule servos are compared with identical outputs from the Comparison Air Data Sensor designed by Elliott Bros. The alarm and disconnect circuits are activated when a discrepancy between the two signals exists.

The aircraft system has duplicated Comparison Air Data Sensors.

Click to enlarge Click to enlarge