Cargo Smoke at FL350: Weight Versus Fire
FL350, M0.78, 120 nm from an airport with an 11,000-ft runway and full ARFF coverage; weather CAVOK, wind calm. The aft cargo smoke detector triggers. You discharge the bottle; 90 seconds later the warning returns. Cabin altitude is normal at 7,800 ft and the cabin crew reports no smoke in the cabin. Gross weight is 8,000 lb above maximum landing weight; the AFM requires an overweight landing inspection above 6,000 lb over MLW, and the airplane is controllable. Fuel is 9,000 lb. A diversion airport 40 nm closer has a 6,000-ft runway and no ARFF. ATC offers FL310 to avoid weather ahead.
1. State your immediate actions and priorities.
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Aviate, navigate, communicate, then mitigate. Fly the airplane, declare an emergency, and start down while running the smoke/fire checklist: confirm the bottle discharge, close the affected valves, remove electrical power from the cargo area, and configure for smoke removal.
The priority order matters. A second detector warning after bottle discharge is evidence of a fire that is not out, and the checklist for an uncontrollable cargo fire assumes the airplane will be on the ground soon. That means the descent begins now and the diversion decision is made in parallel, not after the checklist is complete. Time is the scarce resource; altitude, route, and passenger comfort are not.
2. Should you land overweight? What changes on the approach and after landing?
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Yes. An 8,000-lb overweight landing is an inspection and maintenance event; an uncontrolled cargo fire is a hull loss event. The AFM threshold at 6,000 lb over MLW means the landing will require an inspection, but it does not prohibit the landing.
What changes:
- Approach speed is higher, so touchdown and stopping distance increase; use the longest suitable runway and avoid a tight approach.
- Brake energy is higher; plan for a long rollout and consider whether the runway has the length for a rejected landing at that weight.
- Do not delay the landing to burn or jettison fuel. Fuel dumping, if available, takes time you may not have and may not be permitted at low altitude.
Brief the cabin crew for an emergency evacuation on landing and have the ARFF equipment meet the airplane.
3. Which airport do you choose, and how do you handle ATC's offer of FL310?
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Choose the 120-nm airport with 11,000 ft and ARFF, not the closer 6,000-ft field with no firefighting capability. At an overweight landing weight, 6,000 ft with no ARFF and no equipment to handle a cargo fire gives away the two things that matter most: stopping distance and post-landing fire response. The extra 80 nm is a small price for both.
Decline FL310. Leveling off or climbing with an active cargo fire keeps you at altitude and delays the landing, and the offer was made to avoid weather, not to solve your problem. Tell ATC you are descending now, request a heading and priority to the 11,000-ft airport, and ask for ARFF to be alerted. If the smoke situation worsens, declare the need for an immediate descent and vectors; the controller can move traffic, but only if you say so plainly.