Sequencing a Fast Jet Behind a Slow Turboprop into Nairobi
At 0615 UTC, Nairobi Approach is sequencing two arrivals for JKIA runway 06 in calm winds and 10 km visibility. KQA410, a Boeing 737-800, is 18 NM final at FL110, descending, and has been cleared to 7,000 ft. Jambojet 601, a Dash 8 Q400, is 10 NM final at FL090, 30 kt slower, and has requested a straight-in approach. The aerodrome controller reports the preceding E190 is still on the runway and will vacate at B4, but may need 40 seconds. The B738 is catching the Dash 8 rapidly. The approach radar is serviceable, and 5 NM radar separation is available. The tower has not yet issued a landing clearance to either aircraft. You are the approach controller with no adjacent arrival sector to take one aircraft.
1. What sequence and initial instructions would you issue, and what separation assumptions are you making?
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Sequence the Dash 8 ahead because it is slower and closer to the threshold; placing the B738 ahead would force the Dash 8 to follow a faster aircraft and create compression on final. Both are medium wake category, so apply 5 NM radar separation and do not let the B738 close inside 5 NM. Issue: 'Jambojet 601, continue approach runway 06, maintain 160 kt until 4 NM'; 'KQA410, reduce to 180 kt, maintain 5 NM behind the Dash 8, expect landing clearance at 3 NM.' Do not issue landing clearance to KQA410 until the preceding E190 has vacated; a landing clearance does not protect against runway occupancy. If the E190 has not vacated when the Dash 8 crosses the threshold, send the Dash 8 around and keep the B738 at or above 2,000 ft until resequenced. The key assumption is that the Dash 8 can hold 160 kt to 4 NM; if not, the plan must change immediately rather than relying on the B738 to slow below stable approach speed.
2. The Dash 8 reports unable 160 kt and the B738 reports unable 160 kt. What are your options and which do you choose?
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Compression is no longer manageable by speed control. Options in order: (1) slow the Dash 8 to minimum safe speed and give the B738 a small vector or offset to add track miles; (2) orbit or hold the B738 at 4,000 ft; (3) send the B738 around and resequence it behind the Dash 8. Do not reduce below 5 NM. Because the Dash 8 is ahead and slower, the B738 must be taken out of the final approach path before separation is lost. Coordinate with tower to delay the Dash 8's landing clearance if runway occupancy is still unresolved. Choose the option that preserves a stable approach; a go-around is preferable to a rushed, unstable approach or a loss of separation. If the B738 is sent around, instruct it to climb to 4,000 ft and turn to a safe heading, then sequence it after the Dash 8.
3. Give the key phraseology for the conditional landing clearance and for the go-around.
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Conditional clearance: 'KQA410, runway 06, land after the vacating E190, runway vacated reported.' If the condition is not met by the threshold, cancel the clearance and issue: 'KQA410, go around, climb to 4,000 ft, turn right heading 120, contact Approach 124.7.' For the Dash 8 if runway occupancy is not resolved: 'Jambojet 601, go around, climb to 3,000 ft, turn left heading 090, contact Approach 124.7.' The phraseology must make clear that the landing clearance is conditional on the runway being vacated, not merely on the preceding aircraft being told to vacate. The go-around instruction must include climb, heading and frequency so the crew has a complete missed-approach clearance.