Aircraft preparation for service begins and ends with a thorough inspection of the aircraft exterior. The aircraft, and especially its surfaces providing lift, controllability and stability, must be aerodynamically clean. Otherwise, safe operation is not possible.
An aircraft ready for flight must not have ice, snow, slush or frost adhering to its critical flight surfaces (wings, vertical and horizontal stabilizers and rudder).
Nevertheless, a frost layer less than 3mm (1/8 inch) on the underside of the wings, in the area of fuel tanks, has been accepted by the Airworthiness Authorities without effect on takeoff performance, if it is caused by cold fuel (low fuel temperature, OAT more than freezing and high humidity). Also a thin layer of rime (thin hoar-frost) or a light coating of powdery (loose) snow is acceptable on the upper surface of the fuselage.
Refer to Flight Crew Operating Manual:
Aircraft Type  Chapter  Subject 
A300 GE  8.03.14  PROCEDURES AND TECHNIQUES Inclement weather operations - Aircraft preparation for cold weather operation 
A300 PW  8.02.11 
A300 FF  2.02.09 
A310 A300-600  2.02.13 
A320 family A330 A340  3.04.91  SUPPLEMENTARY TECHNIQUES Adverse weather - Cold weather 

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B3.3.2 External inspection
An inspection of the aircraft must visually cover all critical parts of the aircraft and be performed from points offering a clear view of these parts.
In particular, these parts include:
.
Wing surfaces including leading edges,

.
 Horizontal stabilizer upper and lower surface,

.
Vertical stabilizer and rudder,

.
 Fuselage,

.
 Air data probes,

.
 Static vents,

.
 Angle-of-attack sensors,

.
 Control surface cavities,

.
 Engines,

.
 Generally intakes and outlets,

.
 Landing gear and wheel bays.

B3.3.3 Clear ice phenomenon
Under certain conditions, a clear ice layer or frost can form on the wing upper surfaces when the aircraft is on the ground. In most cases, this is accompanied by frost on the underwing surface. Severe conditions occur with precipitation, when sub-zero fuel is in contact with the wing upper surface skin panels. The clear ice accumulations are very difficult to detect from ahead of the wing or behind during walk-around, especially in poor lighting and when the wing is wet. The leading edge may not feel particularly cold. The clear ice may not be detected from the cabin either because wing surface details show through.
The following factors contribute to the formation intensity and the final thickness of the clear ice layer:
.
Low temperature of fuel that was added to the aircraft during the previous ground stop and/or the long airborne time of the previous flight, resulting in a situation that the remaining fuel in the wing tanks is below 0° C.
　
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