Modification of the estimated off block time (EOBT)

1. Introduction

It is a prime requirement for both ATC and ATFM, that the EOBT of a flight shall be an accurate EOBT. This applies to all flights, whether subject to ATFM or not.

These procedures are to enable an AO to meet this requirement whenever they know that the EOBT of a flight will require modification.

The ICAO requirement is that delays in excess of thirty (30) minutes should be communicated (cf. para. 4.4.2.1.2. ICAO Doc. 4444). This requirement is mandatory. As from the 1st April 2002 onwards, the rules concerning modification to an EOBT for flights, which are departing, arriving or over-flying ECAC-states (IFPS-zone) will change: the requirement in Europe is that any change (+ or -) in an EOBT of more than 15 minutes shall be communicated.

There are two categories of flights concerned: those, which have an ATFM slot, issued by the CFMU, and those who have not. An AO should not modify the EOBT to a later time simply as a result of an ATFM delay. The EOBT is changed only if the original EOBT established by the AO cannot be met by the AO.

2. Procedure of modifying the EOBT of a flight not having received an ATFM slot from the CFMU

Procedure:

To amend the EOBT to a later time, a DLA (or CHG) message shall be sen

To amend the EOBT to an earlier time, a CNL message shall be sent to IFPS followed five minutes later by a new flight plan with the new EOBT indicated.
Note: The replacement flight plan procedure shall not be used.

3. Procedure for modifying the EOBT of a flight, which has received an ATFM slot from the CFMU

AOs should note that an EOBT should not be modified simply in response to any possible delay due to an ATFM slot. If the EOBT established by the AO can no longer be met for reasons other than ATFM, then:

If the EOBT of a flight has changed or is no longer realistic then the following procedure shall be used:

" If a flight has an ATFM slot (CTOT) which cannot be met, then the AO shall send a DLA (or CHG)message to IFPS with the new EOBT of the flight. This may trigger a revised CTOT.

" If a flight has an ATFM slot (CTOT) with some delay and the AO is aware that the original EOBT cannot be met but the existing CTOT is acceptable then a DLA (or CHG) message shall be sent to IFPS with the new EOBT of the flight. However, in order not to trigger a new CTOT with a worse delay, the following formula shall be used:

Take the current CTOT, minus the taxitime, minus 10 minutes and send the new EOBT, which must not be after this time e.g. EOBT 1000, CTOT 1100, but the flight cannot go off blocks until 1025. The taxitime is say 15 minutes. 1100 – 15, minus 10 = 1035. The new EOBT must be earlier than 1035. If it is, then this action will not trigger a revised CTOT.

" However, as CFMU systems are continuously seeking to give zero delay, the CTOT of the flight will never be earlier than the new EOBT plus the taxitime.

" If a flight has had an ATFM slot (CTOT) but now receives an SLC (Slot Cancellation Message) but the original EOBT can no longer be met, then the AO shall communicate the new EOBT by use of a DLA (or CHG) message. ATC/ATFM will now have the “true” EOBT of the flight

" AOs are strongly requested not to use the SRR message (shortly to be deleted from use) to obtain a new ATFM slot (CTOT) but to use the DLA (or CHG) message instead so as to ensure compatibility between ATC and ATFM data.

Some states outside the CFMU area of responsibility still require AOs to update the EOBT regardless of why the flight’s original EOBT may have changed. AOs should bear in mind the formula explained above when doing this. Where it is known that ATC send departure messages (DEP) for all flights, then this DEP message will suffice.

It is not possible to amend the EOBT to an earlier time than the EOBT given in the flight plan however, if a flight is ready to go off blocks earlier than the current EOBT, then there are two options available:

" The AO may ask the local ATC Unit (TWR) or the FMP to send a Ready (REA) message. In this case, the flight is considered as “ready to depart” from the filing time of the REA message.

" The AO may contact Central Flow Help Desk who have the possibility to input an earlier EOBT into the TACT system (max –30 minutes). Each case is treated on its merits and may be refused if it is considered that " abuse" is involved.

This change will be included in the regulation for ATFM presently under revision.

For further information, please contact:

Jan-Gunnar Pedersen
Norwegian Air Traffic and Airport Mangement

Phone: +47 22 94 23 36
Fax: +47 22 942397
Mob: +47 97194853
E-mail: jan-gunnar.pedersen@lv.no