Editing Indicated airspeed (section)

==IAS and V speeds==

The aircraft's pilot manual usually gives critical [[V speeds]] as IAS, those speeds indicated by the airspeed indicator. This is because the aircraft behaves similarly at the same IAS no matter what the TAS is: E.g. A pilot landing at a [[hot and high]] airfield will use the same IAS to fly the aircraft at the correct approach and landing speeds as when landing at a cold sea level airfield, even though the TAS must differ considerably between the two landings.

Whereas IAS can be reliably used for monitoring critical speeds well below the speed of sound this is not so at higher speeds. An example: Because (1) the compressibility of air changes considerably approaching the speed of sound, and (2) the speed of sound varies considerably with temperature and therefore altitude; the maximum speed at which an aircraft structure is safe, the [[Vne|never exceed speed]] (abbreviated ''V''<sub>NE</sub>), is specified at several differing altitudes in faster aircraft's operating manuals, as shown in the sample table below.

{| class="toccolours" border="1" cellpadding="4" style="border-collapse:collapse"
|- bgcolor="#dedede"
|'''Diving below'''
|'''IAS <br/>mph'''
|'''IAS <br/> km/h'''
|-
|{{cvt|30000|ft|m}}
| 370
|595
|-
|{{cvt|25000|ft|m}}
| 410
|660
|-
|{{cvt|20000|ft|m}}
| 450
|725
|-
|- valign="top"
|{{cvt|15000|ft|m}}
| 490
|790
|-
|{{cvt|10000|ft|m}}
| 540
|870
|}

Ref: ''Pilot's Notes for [[Hawker Tempest|Tempest V]] [[Napier Sabre|Sabre IIA]] Engine''  - [[Air Ministry]] A.P.2458C-PN