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Early clearance and fast approach led to Tenerife conflict

Spanish investigators have disclosed that an Iberia Airbus A321 had been approaching Tenerife South airport at high speed just before it landed on the same runway that a Jet2 Boeing 757-200 was departing.

But it believes a premature take-off clearance to the 757 primarily contributed to the incident.

Although the 757 became airborne it had not crossed the opposite end of runway 08 before the A321 touched down.

Spanish investigation authority CIAIAC found the A321's airspeed on final approach had been "considerably higher than expected", even for a decelerated approach profile in which flap deployment is delayed.

Iberia operations specifies that aircraft conducting such approaches must begin the final approach phase with flaps at 10° and an airspeed typically around 180-203kt, to ensure proper speed and configuration by 1,000ft.

The A321's airspeed was 215kt at the final approach point - 5.7nm from the threshold - where the initial flap extension begins for a decelerated approach profile.

At around the same time the 757 had been cleared for an immediate take-off from runway 08, although the aircraft was 300m from the holding point.

Some 35s after receiving the clearance the 757 reached the holding point, by which time the approaching A321 was 3.8nm from the threshold. Although the A321's airspeed had decreased constantly through the descent, its ground speed was still 210kt.

CIAIAC points out that the controllers cannot apply speed control to an aircraft within 4nm of the threshold. It adds that the absence of steady easterly winds which normally slow aircraft approaching runway 08.

The 757 entered the runway and began its take-off run while the A321 was 2.4nm away, and rotated as the A321 crossed the threshold. Analysis showed the aircraft were separated by 1,250m (4,100ft) at their closest point.

Investigators found the Iberia crew, which had the 757 in sight, considered a go-around but felt that continuing the approach was the safer course of action. The A321 crossed the threshold at 155kt.

CIAIAC attributes the 12 November 2011 incident to the tower controller's "improper handling" of the take-off clearance to the 757, given while the aircraft was still "some distance away" from the hold point "without [the controller's] being cognizant of this fact".

Given the A321 had covered over 2nm before the 757 reached the runway, it adds, a measure to limit the approaching aircraft's speed would have been "justified".

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