Response to a "PULL UP" Warning
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Revision as of 21:43, 22 May 2009 by Validator1 (new draft article)
The ‘PULL UP’ audio and visual ‘Hard’ warning generated by GPWS/TAWS or GPWS/TAWS systems is an absolutely vital safety net. Every pilot should understand that their response should be rapid and instinctive. Such a callout is not a time to ask the question ‘why? or to ever assume that the activation might be a false one.
Provided that the database it contains is kept up to date and the equipment is provided with accurate position data by internal or external Global Positioning System (GPS) feed, any correctly functioning TAWS system fitted to an aircraft will provide a reliable protection against inadvertent closure with terrain or an obstruction provided that response is appropriate.
Since the older GPWS systems do not have a position feed or a terrain database, the ‘PULL UP’ Warnings which they generate may not be enough to prevent terrain impact even if actioned properly but an appropriate response still represents the best significant chance of survival.
The standard flight crew response to a ‘PULL UP’ warning
The appropriate response to a TAWS or GPWS ‘PULL UP’ warning for a particular aircraft type will be found in the Aircraft Flight Manual (AFM) or Pilot Operating Handbook. This will be a Memory Drill and will be replicated in the Operations Manual in the case of an aircraft employed in public transport.
However, the principles of any such response will be found in all such drills. The promulgated escape manoeuvre will aim to ensure the establishment of the maximum angle of climb. It must be initiated immediately with the following sequence of actions:
- Disconnect the Autopilot and Auto-throttle if engaged
- Advance the Thrust or Power levers to the Take Off position
- Rotate the aircraft to a pitch up angle which reaches the margin of stick shaker activation. This is likely to be around 20 degrees pitch up for most aircraft
- If speed brakes are deployed, retract them
- If the Landing Gear is selected down, raise it
- If trailing edge Flaps are deployed, raise them one stage
The maximum climb angle achieved must be maintained until the flight crew are sure that the aircraft is above the applicable Minimum Sector Altitude or until it is visually apparent without any doubt that the aircraft is clear of terrain and obstacles. The risk that pressure altimeters might have been mis-set or that the aircraft may not be in the position previously expected should be born in mind when determining that these conditions have been met.
Some Fly by Wire aircraft types may have systems for automatic acquisition of a maximum angle if climb such that the generic sequence above may not apply. Reference should always be made to the memory drill contained in the AFM for the aircraft type.
More generally, some Operations Manuals may permit an exception to the standard response if it is possible to instantly recognise that certain criteria are met at the point at which a ‘PULL UP’ Warning occurs. These are usually if:
(1) The aircraft is definitely above MSA at the time the warning occurs
(2) The aircraft is on final approach below 1000 ft aal with the landing runway in sight, the landing checklist has already been completed, the aircraft is stabilised on the correct vertical profile and in all other respects it is immediately obvious to both flight crew that their aircraft is not in danger because of it’s configuration, proximity to terrain or flight path
Unservisability of TAWS / EGPWS equipment
It is common for an aircraft Minimum Equipment List (MEL) to allow despatch with an unserviceable TAWS or GPWS system. If this is the case, the MEL entry often specifies that ‘alternative procedures are to be established and used”. These may be fully specified in an associated Operations Manual or that Manual may simply give guidance on the action to be taken according to the specifically intended flight. This may include prohibition of flights into and out of particular airports under certain meteorological conditions or by night.
Reporting of TAWS/GPWS ‘PULL UP’ Warnings
All flight crew who receive a ‘PULL UP’ warning should raise an Air Safety Report (ASR) detailing all known circumstances. ATCOs who become aware of such occurrences should do likewise and their organisation should then advise the Operator. Aircraft Operators with a flight data monitoring programme should have an automatic alerting system for any recording which contains such an occurrence and this should support an investigation already initiated by receipt of an ASR or prompt the commencement of a new investigation.
Related Accident & Serious Incident Reports
See relevant CFIT category examples (select appropriate direct references)