One Reverser Inoperative, a Contaminated Forecast and a 500 kg LMC
Your twin-jet is at the gate with 172 passengers. The MEL permits dispatch with one thrust reverser inoperative, provided the landing distance is multiplied by 1.15 and the runway is dry; dispatch is not permitted to an aerodrome where a contaminated runway is forecast at ETA. Destination runway 24 has 2,300 m available because of works (declared LDA reduced from 2,600 m). Actual landing distance at the planned landing mass is 1,450 m. The TAF gives wind 240/12, visibility 6,000 m, rain and snow showers, temperature +1 C, QNH 1005, temporarily 2,000 m in snow. The runway is dry now, but the previous aircraft reported braking action medium on the last 800 m, and the aerodrome operator expects 2 mm slush if the showers arrive. During boarding, 800 kg of late cargo is loaded although the load sheet was made for 300 kg; the commander is told the trim will not change.
1. Is the dispatch valid under the MEL? Show the performance calculation and the operational conditions.
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Dry-runway performance: 1,450 x 1.15 = 1,667.5 m required against 2,300 m available, a margin of about 632 m. On a dry runway the performance case is comfortably acceptable. But the MEL condition is not met. The item is allowed only if the runway is dry and no contaminated runway is forecast at ETA. The TAF contains rain and snow showers at +1 C, temporary visibility 2,000 m in snow, and the aerodrome operator expects 2 mm slush. A contaminated runway is therefore forecast. The previous aircraft's braking action medium on the last 800 m also shows the runway is not uniformly dry now. Conclusion: dispatch to this destination is not permitted under the MEL, whatever the dry-runway arithmetic shows. The 1.15 factor is an additional condition, not a substitute for the dry-runway condition. Options: restore the reverser if the defect can be cleared; change destination to an aerodrome with a dry runway forecast at ETA and adequate fuel and alternate; delay until the forecast no longer shows contamination; or cancel. 'We will land on the dry part' or 'we will take it if it is only wet' is not an acceptable dispatch decision. If the flight is dispatched, the commander must be satisfied that the actual condition on arrival will meet the MEL, and a later change requires a re-plan, not a rationalisation.
2. How should the last-minute change be handled? What limits and performance checks apply?
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The load sheet no longer matches the aircraft. 800 kg loaded against 300 kg on the sheet is a last-minute change of +500 kg. The commander signs for the load sheet, so a verbal assurance that 'the trim will not change' is not enough. Check in this order:
- Operator's LMC limit - commonly 500 kg, but often lower, and only if the CG remains within limits and the change can be entered on the load sheet by hand. At +500 kg you are at or beyond many limits, so a new load sheet is the safe answer. Recompute CG and trim; 500 kg in the wrong hold can move the CG significantly.
- Mass limits - MTOM, MLM, MZFM and takeoff performance at the actual mass, including takeoff run, climb gradients and obstacle data.
- Landing performance - recompute the actual landing distance at the new landing mass rather than adding a percentage. The 1.15 reverser factor still applies and the dry-runway condition still applies.
- Fuel - the higher mass increases trip fuel, so check that the fuel plan still meets the reserve. Document the change and tell the loading supervisor. Do not depart with a load sheet that misstates the load; the commander's signature certifies the figures.
3. If the flight departs and the destination is contaminated on arrival, what do you do?
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Do not land on a contaminated runway. The MEL condition is an operating limitation, not a recommendation. If the runway is contaminated (standing water, slush, snow, or braking action below good), the aircraft is not permitted to land there with one reverser inoperative, regardless of the arithmetic. The correct decision is to hold only if a dry runway is expected within the protected fuel; otherwise divert to the planned alternate or another suitable aerodrome with a dry runway. Before departure, brief the arrival threat: contaminated runway, one reverser, reduced LDA and diversion fuel. On arrival, get the current runway condition from ATC or ATIS, not from the TAF. If the report is contaminated, request the diversion early, while fuel and alternates are comfortable. If fuel becomes critical while diverting, use the standard declarations (MINIMUM FUEL, then MAYDAY FUEL), but the fuel problem would be a consequence of not diverting early. The decision must be made before the fuel is tight; the MEL does not become more permissive because the destination is inconvenient.