Flexible use of the PMS method

Concerning the flexible use of the method the results of the second and third prototyping sessions have completely confirmed what already came out during the first study.

The controllers involved in all the studies have often highlighted that introducing the PMS method may imply a certain loss of flexibility with respect to the open loop vectors currently used (par. 3.1). Nonetheless this loss of flexibility has been considered acceptable because counterbalanced by evident benefits in terms of

workload reduction and efficiency of the arrival traffic management.

In addition one other reason contributed to make the method acceptable and domain suitable for the controllers. It was the possibility of a flexible use of the method.

In the previous paragraphs, the effectiveness of the PMS method has been described as strictly dependent on the application of its basic principles, namely:

• the pre-sequencing according to which the upstream sectors hand the traffic over to TMA sectors with a spacing of at least 7NM, steady and at predefined speed and flight level,

• the use of first in first out principle and distance ring while the aircraft is in the triangle

• the association between triangle and runway (but for cases of pilot’s request and runway balancing)

• the use of triangles capacity, segments of the sequencing leg and triangles as trigger for SM LIRF intervention (whose need came out during the study). In general the respect of these rules guarantees the successful application of the method. Nonetheless it may also happen that these rules are violated. In these cases all the prototyping sessions have revealed that the method can be quite flexible.

Some cases have been observed during the prototyping sessions in which the method has been successfully applied notwithstanding violations in the application of its basic rules. In particular these cases concerned:

• violation of the pre-sequencing rule

Two different cases of inappropriate pre-sequencing have been observed during the study.

In the first case 2 aircraft have been handed over to TN sector one above the other, meaning that they entered in the sequencing leg at the same time and on the same point, but at different flight levels. TN controller managed the situation in two steps. He quite soon instructed the first aircraft (that was steady at the pre-defined flight level) to turn to the merge point and then to descend. He left the other one continuing to descend to the flight level of the sequencing leg while flying through it. When the first aircraft reached the distance ring, he

cleared the other aircraft direct to merge point instruction and then descent. In the second case the inappropriate pre-sequencing affected most of the inbound traffic to LIRF, since it was due to bad weather in the upstream sectors. Also in this case the controllers continued managing the traffic with PMS, using the sequencing leg to appropriately sequence the traffic. They found the method comfortable and reliable. They also claimed that the key element for the effective application of such flexible use of the sequencing leg was the respect of the triangle capacity (par.3.2.1).

• violation of the first in first out rule

In this case two aircraft entered opportunely pre-sequenced in the sequencing leg. Since the first one was Heavy, the TN sector controller decided to violate the first in first out rule. As consequence he gave the direct to merge point instruction to the second aircraft first and then to the other in order to profit by a hole in the sequence.

• violation of the association between triangle and runway

In this case SM LIRF coordinated with the upstream sector controller that one traffic coming from North-West and expected to land on East runway was managed within the West triangle and then, after FRANK/VANIA sent to East runway. The upstream sector controller managed it accordingly, handing it over to the TN sector controller opportunely separated from traffic to the West runway. The TN sector controller, knowing that the two aircraft were expected to land in two different runways, and in agreement with the SM LIRF, gave the direct to instruction to the two aircraft almost at the same time. He then instructed them the descent to two different flight levels: 5000 to the aircraft landing on the West and 6000 to the other one. He then instructed this latter to further descend to 4000ft after the point merge.

• Vectoring inside the triangles

In this case some aircraft have been radar vectored inside the triangles, while flying from one distance ring to the other in order to adjust the sequence or to create the spacing for a go around to be inserted. Similarly other flights have been slightly vectored in the final path for spacing or to be re-routed to the

West runway – in exceptional cases. • Violation of triangles capacity

In this case due to external events (namely go around or runway inspection) the triangle revealed temporary overloaded and some aircraft arrived at the end of the sequencing leg. The TN sector controller radar vectored the traffic, as extending the sequencing leg, and then re-inserted them into its part direct to the merge point.

It is interesting to notice that these violations have not been perceived as problematic. On the contrary the controllers tended to consider these cases as a proof of the possibility to use the method in a flexible way when necessary. It was considered an advantage of the technique, that though rigid allows to violate its own rules if necessary and in sporadic cases, well coordinated with SM LIRF. What is interesting to notice is that these violations were considered effective if applied in exceptional situations and well coordinated internally to the team. Conversely they were considered likely to compromise the effectiveness of the method if applied in a systematic way and without coordination with the rest of the team.

The recommendation for the next stage of the project is to include this topic in the training package, clearly highlighting that the method is rigid but seldom can be used in a flexible way if necessary. Systematic violations are not allowed since they are affecting the effectiveness of the method itself.