Standard Operating Procedures and Checklists

Standard operating procedures (SOPs) are the operator's fixed, written way of doing each task on the flight deck: who does what, in what order, and what each pilot says. Checklists are the short written lists that crews read to confirm that the critical steps of a procedure have been done. Both exist because two people who have never flown together must work as one crew from the first minute, and because human memory is least reliable exactly when the stakes are highest.

SOPs are written by the operator, starting from the manufacturer's procedures, and published in the operations manual; under EU rules the aeroplane operating procedures, normal, abnormal and emergency, sit in Part B. ICAO Annex 6 requires the operations manual to contain the normal, abnormal and emergency procedures with the checklists that go with them, and instructions on when and how the normal checklists are used. Light aircraft pilots use the same ideas on a smaller scale, with the checklist in the pilot's operating handbook and, in a flying club, the club's own SOPs.

Purpose of SOPs

The FAA's advisory circular on SOPs, AC 120-71B, calls them the foundation of effective crew resource management. When both pilots know exactly what should happen, who does it and what will be said, any departure from the expected sequence becomes a visible cue that something is wrong. SOPs also make routine actions habitual, freeing attention for threats, and take the question of how to do something out of the critical phases of flight. In the SHELL model they reduce errors at the liveware-software interface, where pilots misread manuals, charts and checklists.

Their limit is that no set of procedures covers every situation. A combination of failures with no checklist forces a crew into knowledge-based reasoning, which is slow and error-prone, and the best response is then to slow the situation down and use every source of help. Their weakness is erosion: a shortcut that "everyone" takes becomes a routine violation, normal precisely because nothing has gone wrong yet. Line operations safety audits find procedural errors, against SOPs, checklists and callouts, the most common kind of crew error (see threat and error management).

Normal, abnormal and supplementary procedures

Manufacturers and operators sort procedures by the situation they serve:

• Normal procedures (NP) cover every flight from preparation to shutdown. Airbus describes its SOPs as inspections, preparations and normal procedures, written on the assumption that all systems work normally and all automatic functions are used normally.
• An abnormal procedure deals with a failure or unusual situation that does not immediately threaten the aircraft; an emergency procedure with one that does. Boeing calls both non-normal procedures. Many are triggered by an alert, but some events, such as many smoke and fumes cases or a tailpipe fire, give no alert and have non-annunciated procedures.
• A supplementary procedure (SP) is a normal procedure needed only in particular conditions: cold weather, operation without the APU, a manual engine start, or the 737's electrical power up procedure, which its preliminary preflight assumes has been done. Embraer's E-Jet QRH groups such supplementary normal procedures in its own section.

Cockpit flows and scan flows

Most normal procedures are done as cockpit flows: sequences of actions from memory that follow the layout of the panels, each pilot covering a defined area of responsibility. Boeing's procedures are done "by memory and scan flow", and Airbus lists the items of each procedure in the order of a standardised scan of the cockpit panels unless that order conflicts with the priority of the actions; the scan flow is that fixed path around the panels. A flow is fast and hard to lose one's place in, because the panel itself is the prompt.

Flows are not checked by memory alone. Checklist discipline, often summarised as flow and check, means doing the flow, then reading the normal checklist, a short list of the items whose omission could be catastrophic, to confirm them. The checklist is called for at defined points, typically before start, after start, before take-off, after take-off, approach, landing, after landing, parking and securing, and by a defined person; on the 737, for example, the preflight checklist is read on the captain's command. It is not started at a moment of high workload: Airbus completes the after landing checklist only once the aircraft has cleared the runway.

Challenge-and-response checklists

In a challenge-and-response checklist, also written challenge-response, one pilot, usually the pilot monitoring, reads each item aloud as the challenge. The other pilot looks at the actual control or indication and gives the response, ideally stating what is seen rather than a bare "checked". Two people are in the loop on every item, which gives redundancy against slips and lapses. It is the method for the critical normal checklists, such as before take-off and before landing. The checklist ends with the call "checklist complete", so that both pilots know where they are.

Read-and-do checklists

A read-and-do checklist is read one item at a time, and each action is carried out before moving on. It is the method for non-normal procedures, where the crew has no flow to fall back on: the pilot flying flies the aircraft, the pilot monitoring reads the checklist aloud and performs or asks for the actions, and both pilots confirm each one, above all those that cannot be reversed. Some operators also use a read-and-do method for lower-risk normal checklists such as after start, and a single pilot uses the written checklist as a do-list for the same reason.

Airbus adds several rules to its ECAM and QRH procedures. After a failure on take-off or go-around, read-and-do actions wait until at least 400 ft above the ground unless the flight path is safe earlier. The pilot monitoring's attention goes to the procedure, so radio communication passes to the pilot flying. Procedures are applied one at a time, and each is completed unless it calls for another procedure or a new, unexpected emergency needs the situation to be reassessed. For a control that the procedure asks the pilot monitoring to operate, the pilot monitoring points to it, the pilot flying confirms, and only then is it moved; the thrust levers stay with the pilot flying.

Checklist discipline

Human factors studies of checklist use keep finding the same errors. The most common is answering items automatically rather than deliberately: pilots who dismiss a checklist quickly see what they expect to see rather than what is there. An interruption, such as a radio call in the middle of a checklist, typically produces an omission, because it breaks the sequence. The defences are simple:

• look at, and where possible touch, each control or indication named;
• after an interruption, go back to a point known to be complete, and to the top of the checklist if in any doubt, rather than resuming from where one thinks one was;
• voice an omission immediately and specifically, rather than correcting it silently;
• never skip a checklist because the sector is short or the crew is late.

The price of a missed item is well known. In 1987 Northwest Airlines Flight 255, an MD-82, crashed on take-off from Detroit after its crew failed to extend the flaps and slats, an item of the taxi checklist, and the take-off warning did not sound. Checklist design matters too: long passages in capitals are slow to read, and red text on a white card can disappear under red cockpit lighting.

Memory items and touch drills

A memory item, or recall item, is an action that must be taken before any checklist can be opened, because seconds count. The list is short and type-specific: donning oxygen masks in a rapid depressurisation, the stall, windshear and terrain escape manoeuvres, the unreliable airspeed pitch and thrust settings, and on the 737 the single aborted engine start action, start lever to CUTOFF. Boeing also marks certain limitations, such as the maximum tailwind for take-off and landing, as items to be known from memory. Once the aircraft is under control, the checklist is read to confirm the memory items and complete the procedure (see A320 memory items).

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Memory items stop at what is urgent. Actions that cannot be undone, such as shutting down an engine, discharging a fire bottle or cutting off fuel, are confirmed by both pilots first. At Kegworth in 1989 a 737-400 crew, reacting quickly to heavy vibration and a smell of burning after a fan blade failed in the left engine, shut down the healthy right engine; the damaged engine lost power on final approach.

A touch drill is the rehearsal of an emergency procedure by touching each control in turn, without operating it. Light aircraft pilots use it to learn their immediate actions after an engine failure, which are done from memory while flying the aircraft, with the checklist used only if time permits. Airline crews use the same idea in non-normal procedures, when the pilot monitoring points to a control and waits for the pilot flying's confirmation before operating it.

QRH and electronic QRH

The quick reference handbook (QRH) is the cockpit book of non-normal checklists and, on many types, of the normal checklists and in-flight performance data as well, such as the unreliable airspeed pitch and thrust tables and landing distances with failures. On Airbus aircraft most failures are handled from the ECAM, and the QRH covers events the electronic alerting system cannot detect, such as many smoke and fumes cases, and procedures the crew starts itself. Some operators put the most time-critical items on a separate quick access card.

An electronic quick reference handbook (eQRH) puts that content on the electronic flight bag. The A320's eQRH application lets the crew run the normal checklists and some abnormal procedures, and gives access to operational data such as the operations engineering bulletins. Whatever the format, the manufacturer's procedure and the operator's SOPs take precedence over any general description, and the managing of a non-normal situation beyond the checklist is covered in managing non-normal situations and diversion.

Library articles are written for study and exam preparation. They do not replace your aircraft's approved documentation, your operator's procedures or the regulations themselves.