Expert: D. Norkus - 6/28/2005

Question
Greetings,

- Could you briefly explain the nature of a dispatcher's job?
- Lets say, the fleet comprises of 10 Boeing 737-400's. Do V-speeds vary with each aircraft?
- Does atmospheric conditions affect the rotation speed of an aircraft?

Thanks

Answer
1)Could you briefly explain the nature of a dispatcher's job?

The Aircraft Dispatcher is a licensed airman certificated by the Federal Aviation Administration. They have joint responsibility with the captain for the safety and operational control of flights under their guidance. They authorize, regulate and control commercial airline flights according to government and company regulations to expedite and ensure safety of flight. They are also responsible for economics, passenger service and operational control of day to day flight operations. They analyze and evaluate meteorological information to determine potential hazards to safety of flight and to select the most desirable and economic route of flight. They compute the amount of fuel required for the safe completion of flight according to type of aircraft, distance of flight, maintenance limitations, weather conditions and minimum fuel requirements prescribed by federal aviation regulations. They prepares flight plans containing information such as maximum allowable takeoff and landing weights, weather reports, field conditions, NOTAMS and many other informational components required for the safe completion of flight.

They  also prepare and sign the dispatch release which is the legal document providing authorization for a flight to depart or can delay and cancel flights if unsafe conditions threaten the safety of his/her aircraft or passengers. They monitor weather conditions, aircraft position reports, and aeronautical navigation charts to evaluate the progress of flight. They update the pilot in command of significant changes to weather or flight plan and recommends flight plan alternates, such as changing course, altitude and, if required, enroute landings in the interest of safety and economy. They disseminate flight information to others in his/her company including stations and reservations. This is the source of information provided to the traveling public.

Dispatchers must undergo extensive training to have earned the coveted Aircraft Dispatcher's certificate having taken and passed both an extensive oral examination and the  comprehensive Dispatch ADX test, administered by the Federal Aviation Administration.  These tests are equivalent to the same Air Transport Pilot (ATP) written and oral examinations that an airline captain must successfully complete.

2)Lets say, the fleet comprises of 10 Boeing 737-400's. Do V-speeds vary with each aircraft?

Yes. The V speeds will even vary for the same aircraft and can be different on every flight (but are usually all within a 30-40 knot range). They are calculated based on the specific takeoff weight for that flight and the temperature at the time. So depending on the load carried and the temp at the field, the same aircraft may not have the same V speeds all day.

Go to this link to see some examples of Boeing 737 V speed calculations-
http://www.b737.org.uk/vspeedcalc2.htm

Here is another great link that uses the 737 as an example-
www.idfreelancejournalist.co.uk/Speeds.pdf

3)[Do] atmospheric conditions affect the rotation speed of an aircraft?
Yes, as mentioned in the V-speed response above temperature is a consideration in calculating V speeds which includes Vr. Vr is also affected by runway contamination and slope. A correction factor of plus or minus a few knots is applied in if the runway has either.