Pinetree Line

1956 – Introduction to Intercept Control – National Archives of Canada


The motto of Air Defence Command is "Detegere et Destruere". In order to achieve this goal the entire Air Defence System is organized to take the necessary actions that all equipment and personnel are coordinated for this purpose.

The first action by the Air Defence system is the detection of electronic returns from airborne objects. This initial pick up , or blip on the PPI, is passed to plotting personnel. It is displayed on a horizontal or vertical plotting board and is assigned a track number. The identification section has two minutes to correlate the track with available information, and identify it as hostile, friendly, or unknown. If friendly, no further action is required other than normal surveillance. If no flight plan, or other information, is available the track is classified unknown. If its speed and altitude are within range of known enemy aircraft then a classification of hostile may be given. The two normal classifications, however, are friendly or unknown.

Unknown aircraft must be forward told by the AC&WS to the next higher echelon, the Sector. Here, a decision on whether to scramble a fighter interceptor, or not to, is made. The scramble prerogative is normally retained at the Sector, but in some cases a delegation of scramble authority to the AC&WS performing the Ground Controlled Intercept function is made. This is usually limited to one fighter with the majority of the available fighters in the Sector retained for tactical decision by the Sector Commander.

When a decision to scramble a fighter is made, a Fighter Controller is assigned by the GCI Duty Controller to control it. The Controller is given his target, the Fighter’s call sign, the radio frequency to be used during the intercept, and the PPI to be used. He then proceeds to establish radio contact with his fighter and gives the pilot the required information on the target prior to turning onto the attack vector. The control phase is a critical period and many factors must be taken into consideration in committing the fighter. The essential items require an initial vector for the target, and a calculation for displacement positioning the fighter on either side of the target. This displacement allows for a final turn, or turns, onto the final attack heading and a short interval to get steady, before the AI equipment is within its maximum range for electronic pick-up of the target. The control at this stage must be precise and brief. The controller’s role is to position the fighter at approximately 90 degrees to the target heading on an angle off from the fighter to target based on relative speeds. When at fifteen miles or less, if the fighter is properly positioned the AI equipment in the fighter is locked-on to the target and the final phase of the intercept is flown by the crew according to radar equipment display. A small scope in the pilots instrument panel shows when a lock-on is made, twenty seconds to go, and the firing phase or a break-off as necessary. After the intercept the fighter continues to fly through for two minutes and then turns to a reciprocal heading to the target and waits for further instructions from the GCI controller.

The next stage of control is recovery to the fighter’s base, or an alternate if weather limitations require it. The fighter is given a steer for base and depending on whether the landing is to be IFR or VFR the required approach clearances are obtained from the control tower at the base.

This clearance becomes more and more urgent depending on the number of fighters requiring recovery action. The Fighter Controller’s job ends with the fighter’s clearance to local control.


This article was obtained from DND DHist. in July 1998 for use on the Pinetree Line web site. There was no date or additional identification on the paper aside from an initial classification stamp of SECRET. Estimated circa 1956