I am writing to you as part of the Public Accounts Committee's inquiry into the work of National Air Traffic Services Ltd and air traffic control in the United Kingdom.
The Committee is interested in flow control initiatives, particularly the procedure known as height capping or level capping. NATS have informed us that they do not keep statistics on the numbers of flights that are height capped and I am hoping that you may be able to assist the Committee.
The Committee would like to obtain an accurate and detailed picture of height capping activity in the United Kingdom in the three years prior to the opening of the Swanwick facility on 22 January 2002 and in the period since then up to the present date. By "height capping activity" I am not referring to those instances initiated by airlines, but rather those instances where height capping is imposed by air traffic control as an air traffic flow management measure.
The Committee very much hopes you will be able to provide detailed information in this area as follows:
1. For how many days has height capping been used at West Drayton where height capping was imposed by air traffic control as a flow control initiative:
(a) in the three years prior to 22 January 2002?; and
(b) in the period since 22 January 2002 to the present date?
2. When height capping has been used at West Drayton where height capping was imposed by air traffic control as a flow control initiative, between which hours was height capping used on each occasion:
(a) in the three years prior to 22 January 2002?; and
(b) in the period since 22 January 2002 to the present date?
3. Since 22 January 2002, for how many days has height capping been used at Swanwick where height capping was imposed by air traffic control as a flow control initiative?
4. When height capping has been used at Swanwick where height capping was imposed by air traffic control as a flow control initiative, between which hours was height capping used on each occasion?
5. In each of questions 1 - 4 above, how many aircraft movements were affected?
I do hope that you are able to assist the Committee in its work and I look forward to hearing from you.
8 July 2003