NATCAONLINE

Before the recent sectorisation of the Lagos controlled airspace an approach control unit controlled all air traffic operating within this vast expanse of airspace assisted by an aerodrome control unit. All flights in-bound into Lagos contacts the approach controller at least ten minutes flying time before entering the Upper Terminal Control Area (UTA) i.e. 100nm and for flights from the west, before TYE1 VOR. He gives air traffic control clearances to all these flights with the objectives of safety, orderliness and expeditiousness serving as his guide. The approach controller transfers the arriving traffic to aerodrome control tower over the clearance limit-'LAG' VOR, vacating the minimum approach altitude of 2200ft on QNH in accordance with part 8.3.4.1.1 of DOC.4444 that "a unit providing approach control service shall retain control of arriving aircraft until such aircraft have been cleared to the aerodrome control tower and are in communication with the aerodrome control tower". The approach controller handles enormous volume of traffic arriving, departing and over-flying without the traditional radar back up.

In arriving at the adoption of vertical sectorisation of Lagos controlled airspace procedurally the following hypotheses may have informed the thinking of ATC authorities.

· That a great relationship exists between the-volume of air traffic and the safety performance of a controller.

· That the safety of flights is predicated on the quality and efficiency of personnel involved in the performance of ATC.

· That the quality and quantity of equipment employed determine safe delivery of ATC instructions. And that all above considerations may have to interact so that delay to traffic may be reduced and controllers' workload may equally be reduced.

SECTORISATION

The above hypotheses and the inherent problems associated with procedural control of air traffic in mind, the appropriate ATS authority arrived at the division of Lagos controlled airspace into two-terminal and approach control units. This is done with the believe that such division would in no small measure reduce the workload of the approach controller. Consequently the terminal control unit handles flights operating at FL160 and above and /or65NM and beyond, while the approach control unit handles all flights at FL150 and below and within 65NM.

TERMINAL CONTROL UNIT

This unit provides positive clearances to all inbound traffic at or above flight level 160 and outside 65NM of 'LAG' VOR until the aircraft has reported passing through that level descending or has come closer than the distance earlier stated whichever is the earliest before the aircraft is transferred to the unit providing approach control service.

All departing aircraft climbing out of FL160 at whatever distance comes under the control of the terminal control unit. This unit assumes control of such aircraft until they check the Upper Terminal Area (UTA) and are transferred to the Flight Information Centre (FIC). And in case of westbound traffic, transfer point is 'TYE' or TENTU' to Accra.

APPROACH CONTROL UNIT

All inbound flights are transferred to the approach control unit by the unit providing terminal control service when such aircraft are within 65NM of 'LAG' VOR or at FL160 whichever is earlier. The approach control unit provides ATC service to such flights until they are transferred out of the initial approach altitude (2200ft) to the unit providing aerodrome control service for landing clearance. For all departing aircraft the aerodrome control tower transfers all departures to the approach control unit immediately the aircraft is airborne. This unit controls such aircraft until passing FL160 OR 65NM whichever is earlier and then transfers such to the terminal control unit. For all aircraft operating below FL160 in and out of the terminal control area (TMA) come under its control until they are transferred to the tower or the FIC for outbound flights. Each of the units described above is expected to be manned by at least two ATCOs with the fifth doing the necessary coordination between the two units on the one hand and between the two units and the tower on the other hand. The coordination with the FIC should necessarily remain constant.

In-between this coordination that telephone calls would have to be answered some bothering on safety. This means that at least five (5) ATCOs are expected to be at hand for the use of terminal and approach control units at any point in time swapping positions when required.

For the reason of alleviating the imminent shortage of manpower this innovation would bring, thirteen (13) controllers were 'recalled' to Lagos. This 'recall ' as it were, brought back those that rated in Lagos with the supposed intention of ease of re- integration into the complex Lagos set-up.

ATCOS EXPERIENCE AND OBSERVATIONS

The new system actually reduces the workload on individual duty controller to a great extent. It contrasts sharply with the time when only the approach controller would control 12 to 16 flights. Same number of flights systematically divided now makes the job easier. It is however observed that more than ever before coordination is the heart of the current system. Coordination of each flight movement with all units involved must be carried with unfailing assiduity. If proper coordination exists, it is observed that the current system is capable of reducing airmiss incidents.

CONCLUSION

Although the sectorisation was done with the intent of reducing workload and stress on controllers it seems to have inadvertently added others while some remained largely unsolved. Among those unsolved is the epileptic nature of the Lagos VOR/ DME resulting from incessant power outages, lack of back-up frequencies in case of blockages or failure. Those created include likely denial in case of any incident because of lack of records on the conversations between approach and terminal control units. The room in which these units are co-located is prone to being noisy as the two units may transmit at the same time. The pilots at the receiving end would have to sieve the information that is meant for him, and the situation is made worse.

By Remi Olajire

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