The equipment, and hence the aircraft, knows where it is at all times. It knows this because it knows where it isn't. By subtracting where it is from where it isn't ( or where it isn't from where it is, depending on which is greater ), it obtains a difference or deviation. The inertial reference system uses deviations to generate corrective commands to fly the aircraft from a position where it is to a position where it isn't. The aircraft arrives at the position where it wasn't; consequently, the position where it was, is now the position where it isn't. In the event that the position where it is now, is not the same as the position where it originally wasn't, the system will acquire a variation. ( Variations are caused by external factors, and discussion of these factors is beyond the scope of this simple explanation.) .
The variation is the difference between where the aircraft is and where the aircraft wasn't. If the variation is considered to be a significant factor, it too may be corrected by the IRS. The aircraft must now know where it was. The "Thought Process" of the equipment is as follows: because a variation has modified some of the navigational information which the aircraft acquired, it is not sure where it is. However, it is sure where it isn't and knows where it was. It now subtracts where it should be from where it wasn't ( or vice-versa ) and by differentiating this from the algebraic difference between where it shouldn't be and where it was, it is able to obtain the difference between its deviation and its variation; this difference being called error.
An award should go to the United Airlines gate agent in Denver for being smart and funny, and making her point, when confronted with a passenger who probably deserved to fly as cargo.
During the final days at Denver's old Stapleton airport, a crowded United flight was cancelled.
A single agent was rebooking a long line of inconvenienced traveller's. Suddenly an angry passenger pushed his way to the desk. He slapped his ticket down on the counter and said, "I HAVE to be on this flight and it has to be FIRST CLASS."
The agent replied, "I'm sorry sir. I'll be happy to try to help you, but I've got to help these folks first, and I'm sure we'll be able to work something out."
The passenger was unimpressed. He asked loudly, so that the passengers behind him could hear, "Do you have any idea who I am?"
Without hesitating, the gate agent smiled and grabbed her public address microphone.
"May I have your attention please?" she began, her voice bellowing throughout the terminal. "We have a passenger here at the gate WHO DOES NOT KNOW WHO HE IS. If anyone can help him find his identity, please come to the gate."
With the folks behind him in line laughing hysterically, the man glared at the United agent, gritted his teeth and swore "(Expletive) you."
Without flinching, she smiled and said, "I'm sorry, sir, but you'll have to stand in line for that, too."
The man retreated as the people in the terminal applauded loudly. Although the flight was cancelled and people were late, they were no longer angry at United.
1. INITIAL ACTION: Determine which seat is running away. During the stress of routine operations it is possible to mistake which seat is running away. Example: If Captain's seat is out of control forward, it shall appeat to the Captain that the First Officer's is running backwards. This is a common form of spacial disorientation and will only last until the Captain is emasculated on the control column. Do not disengage the autopilot at this time as a violent pitch down will result. In order to determine which seat is the runaway, suggested procedure is to awaken the Flight Engineer for trouble shooting.
2. SILENCE AURAL WARNINGS: With the advent of a runaway seat, crew members describe noises of a low rumbling nature followed by the words, "Jesus, my seat is out of control" followed by a piercing scream of increasing intensity and pitch, especially in cases of forward runaways. As in all emergencies and in order to comply with C.A.A standardization, the First Officer will silence the aural warning by clamping a hand over the Captain's mouth and advise, "Capt's mouth SHUT, SHUT". From this point on refer to the check list, located on the under side of the Capt's seat cushion.
3. JAMMED BALLS: Should the seat runaway in the forward mode, the ballbearing's will interlock and jam the seat when it is 4 inches from control panel. The seat will then be stuck in the forward position and travel no further forward but begin traveling up in a vertical mode. The Capt. will advise crew, "I have jammed balls". The Engineer will immediately refer to the CAPT JAMMED BALLS Check List located in the aft lavatory. It is imperative that the crew check for control column damage at this time. If the control column is broken. the crew will advise dispatch that the Capt. has a broken stick and jammed balls.
4. CIRCUIT BREAKER - PULL, PULL: The Engineer at this time will pull the appropriate C/B to prevent the seat from running up further in the vertical mode which could cause the bearings to overheat and possibly result in a Ball Burst. This would necessitate the use of the BROKEN BALLS Check List. Since the Engineer can rarely find the correct C/B it is suggested that any C/B be picked at random and pulled so as not to delay completion of the Check List. Example: Pull V.G #1. Capt's position will prevent him from cross checking this step.
5. FIRE CHECK - CHECK: When the seat bearings jam and stop forward seat travel, the electric motor may short out and start a fire under the Capts seat, resulting in a Capt's lower aft body overheat. The Engineer will advise the Capt. of the fire, to which the Capt will reply, "Fire my Ass".
6. SEAT UP- UP: Should the seat continue to runaway in the vertical mode, the First Officer will advise "Seat UP, UP" to which the Captain will reply "Molxjrmne craxmby". Capt's reply will vary with height to which his seat has risen. It is suggested procedure to place a pillow on the Captain's head, and land at the nearest suitable airport.
British Air Ferries (now British World Airlines) used to operate Viscount 800's on a Shell Oil Contract between Aberdeen UK and Sumburgh in the Shetland Islands. These have just been phased out and replaced with ATR72's, which has prompted the following lyric from one of the regular passengers.
So, fareweel Viscoont, trusty BAF,
They've finally gone and sold ye aff,
Wi' yer nice big windies an' seats so wide,
And four Rolls Royces, two each side,
Now, when we go tae Sun-berra,
Its goin tae be by ATR,
This Franco-'Tally Euro-flyer,
Wi' propellers aff a tumble dryer,
An' concrete seats an' service trolley,
Incorporates one basic folly,
The double turboprop is fine,
Its cheap tae run and doesnae whine,
Yet, deep doon inside, 'twas guid tae know,
That if yin stopped, there wis THREE tae go!.