Aircraft Systems, Emergency Procedures, and Human Factors
Aircraft Systems
What the Dispatcher Must Understand
You will not repair the airplane, but you must know what a system failure does to the release. Engines: N1/N2, EGT, and EPR as thrust references; bleed-air anti-ice costs both thrust and fuel and must be in the performance plan. Fuel: totalizer versus quantity, imbalance limits, crossfeed and jettison considerations. Electrical: IDGs, APU generator, TRUs, battery and essential/standby buses - losing a bus changes what equipment is available for the route. Hydraulics: multiple systems with a power transfer unit or ram air turbine as backup. Pressurization: bleed source, outflow valve, cabin altitude and differential limits - critical for drift-down planning on high-altitude or ETOPS routes. Ice protection: thermal (bleed) versus pneumatic boots versus fluid systems; known icing requires an approved system and a plan.
MEL and CDL
Aircraft may be released with inoperative equipment only under the MEL, which is derived from the MMEL. Categories reflect repair intervals: A as specified in the remarks, B 3 days, C 10 days, D 120 days. A CDL covers missing or altered external items and usually carries a performance penalty (drag, weight, or speed loss). Dispatchers cannot waive an MEL item or extend a category without approved authority.
Weight and Balance
MTOW, MLW, MZFW and CG limits; %MAC inside the envelope. Forward CG raises stall speed and takeoff distance; aft CG reduces stability.
Worked Example
A Category C item is placarded inoperative on the first flight of the day Monday. It may remain inoperative for 10 calendar days, counting the day of discovery - plan the repair by the following Thursday before midnight, and confirm the MEL's operational (O) and maintenance (M) procedures are satisfied.
Emergency Procedures and Human Factors
Emergency Authority and the Dispatcher's Role
The PIC may deviate from the regulations to the extent required in an emergency; that authority belongs to the flight deck, not the dispatch desk. The dispatcher's job is to assist, coordinate, and document: relay information, obtain ATC priority or a clearance, amend or reissue the release, arrange diversion support, and initiate the company emergency plan. If contact cannot be established and circumstances warrant, the dispatcher declares the emergency and notifies ATC and company management. Times and decisions must be logged - they become the record after the event.
Know the classic scenarios: decompression and emergency descent, engine failure or fire, diversion and ETOPS diversion to an adequate airport, fuel dumping, hijack and bomb-threat handling, and accident notification under NTSB Part 830.
Human Factors
Fatigue is the dispatcher's biggest threat: sleep debt, circadian low points (roughly 0300–0600 local), and long duty periods degrade vigilance and calculation accuracy. Add stress, workload spikes during weather events, complacency with automation, and communication breakdowns between shift, crew, and maintenance. Defenses include Dispatch Resource Management (DRM), structured briefings, checklist discipline, and structured decision models such as DECIDE.
Traps
- Assuming the dispatcher can order a diversion - you can recommend, coordinate, and refuse to release, but the PIC decides in flight.
- Forgetting that declaring an emergency is a communication act, not a regulatory violation.
Worked Example
A flight is 30 minutes past its ETA with no contact. Attempt contact through company, ARINC, and ATC; confirm the aircraft's last reported position and fuel state; then declare an emergency and activate the company response plan, noting every time.