Clearance

clearance

1. 

a. the disposal of merchandise at reduced prices

b. (as modifier): a clearance sale

2. the act of clearing an area of land of its inhabitants by mass eviction

3. Dentistry the extraction of all of a person's teeth

4. a less common word for clearing

Clearance

 

the maximum profile of an object. As applied to transport vehicles and the moving parts of stationary machines, clearance is determined on the basis of their safe movement among other machines and structures. Outside the clearance, which permits the movement of machines in different directions, it is possible to erect structures and set up machines, lathes, and the safety zone for people. For example, the clearance of a moving train is the maximum profile in a plane perpendicular to the axis of the railway track beyond which no part of a locomotive or car should project when in working order. A railway clearance gauge is the maximum profile in a plane perpendicular to the axis of the railway track within which no parts of structures and equipment should extend. Meeting these clearances ensures the safe movement of trains in tunnels, on bridges, and under over-bridges. Underbridge clearance is the profile of the clear opening under a bridge between the bottom of its span structure and the estimated navigable level in height and between the supports of the span in width.

REFERENCES

Evgrafov, G. K., and N. N. Bogdanov. Proektirovanie mostov. Moscow, 1966.
Evgrafov, G. K., and N. N. Bogdanov. Zheleznye dorogi. Moscow, 1968.
Evgrafov, G. K., and N. N. Bogdanov. AvtomobiV. Ekspluatatsiia i remont. Entsiklopedicheskii slovar’-spravochnik. Moscow, 1968.

I. A. IVANOV

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Clearance

 

the distance from ground level (plane of reference) to the lowest structural member of a motor vehicle, excluding the wheels; one of the parameters that determine the operational trafficability of motor vehicles.

The minimum permissible clearances established in the USSR are 200 mm, 240 mm, 260 mm, and 270 mm for fully loaded trucks with carrying capacities of 1.5 tons, 3 tons, 5 tons, and 8-12 tons, respectively, and 240-270 mm for buses, depending on their length and purpose.

clearance

[′klir·əns]

(engineering)

Unobstructed space required for occasional removal of parts of equipment.

(mechanical engineering)

In a piston-and-cylinder mechanism, the space at the end of the cylinder when the piston is at dead-center position toward the end of the cylinder.

The ratio of the volume of this space to the piston displacement during a stroke.

(mining engineering)

The space between the top or side of a car and the roof or wall.

(navigation)

The clear space between a vessel and an object such as a navigation light, hazard to navigation, or another vessel.

A specific message from air-traffic control to a pilot of an aircraft allowing him to proceed in accordance with the flight plan which the pilot had filed, or with some modification of the original plan.

In the instrument landing system, the difference in the depth of modulation which is required to produce a full-scale deflection of the course deviation indicator needle in any flight sector outside the on-course sectors.

(ordnance)

Elevation of a gun at such an angle that a projectile will not strike an obstacle between the muzzle and the target.

(petroleum engineering)

The annular space between down-hole drill-string equipment, such as bits, core barrels, and casing, and the walls of the borehole with the down-hole equipment centered in the hole.

clearance

1. Open space between two elements of a building to aid in proper placement, to compensate for minor inaccuracies in cutting, or to allow unobstructed movement between parts.

2. The space or distance allowed for anchorage or erection processes or to accommodate dimensional variations in the building structure.

3. See door clearance.

air traffic control clearance

Authorization for an aircraft to proceed under conditions specified by an air traffic control unit (ICAO). This is to prevent collisions between known aircraft. The pilot-in-command of an aircraft must not deviate from the provisions of VFR (visual flight rules) or IFR (instrument flight rules) air traffic clearance except in an emergency or unless an amended clearance has been obtained. Additionally, the pilot may request a different clearance if he or she has information available that makes another course of action more practical or if aircraft equipment limitations or company procedures forbid compliance with the clearance issued. Pilots may also request clarification or amendment, as appropriate, any time a clearance is not fully understood or is considered unacceptable because of safety. Controllers should, in any such instance and to the extent of operational practicality and safety, honor the pilot's request. The pilot is responsible for requesting an amended clearance if ATC issues a clearance that would cause him or her to deviate from a rule or regulation, or, in the pilot's opinion, would place the aircraft in jeopardy. Normally, only the word clearance is used, and it may be prefixed by words such as start-up, taxi, takeoff, departure, approach, or landing to indicate the particular portion of flight to which the ATC clearance relates. Also called an air traffic clearance.