What is the difference between a checklist and a do-list in airline operations?

A do-list (or flow pattern) is a memory-based sequence of actions a pilot performs to configure the aircraft during a given phase of flight. A checklist is a verification tool used afterward to confirm that every item in the flow was completed correctly. AC 120-71B recommends this distinction because using a checklist as a do-list is slower and more prone to interruption-induced errors.

Why do airline SOPs matter for Crew Resource Management (CRM)?

SOPs create a shared mental model between crewmembers who may never have flown together before, reducing ambiguity about who does what and when. This common baseline frees cognitive resources for genuine problem-solving during abnormal situations. AC 120-71B notes that allowing routine SOP deviations — even harmless-seeming ones — erodes the standardization framework and contributes to normalization of deviance, a well-documented accident precursor.

What is the sterile cockpit rule and how does it relate to SOPs?

The sterile cockpit rule, codified in 14 CFR §121.542 and §135.100, prohibits nonessential activities and duties during critical phases of flight — defined as all ground operations involving taxi, takeoff, and landing, and all other flight operations below 10,000 feet MSL except cruise flight. Well-designed SOPs integrate this requirement naturally by scheduling briefings, non-essential communications, and administrative tasks for cruise altitude, ensuring the crew is not inadvertently placed in a position to violate the regulation.

Standard Operating Procedures and the Value of Crew Standardization

When two pilots who have never met walk up to an airliner together, what prevents confusion, missed steps, and catastrophic misunderstandings? The answer is Standard Operating Procedures (SOPs) and crew standardization — the deliberate, systematic framework that ensures every qualified crewmember thinks, communicates, and acts in a predictable, validated way. Advisory Circular 120-71B, Standard Operating Procedures and Checklists for Commercial Operators, is the FAA's primary guidance document on how operators should develop, implement, and evaluate SOPs and checklists. Understanding this framework is essential for any Airline Transport Pilot (ATP) candidate, because it underpins virtually every element of Crew Resource Management (CRM).

Standardization does not mean robotic uniformity or the suppression of good judgment. Rather, it creates a shared mental model — a common baseline of expectation — so that when judgment is required, the crew can focus cognitive resources on the problem rather than on decoding each other's intentions. This is the operational genius of well-designed SOPs: they reduce workload during high-stress moments by making the routine genuinely routine.

What Are Standard Operating Procedures?

SOPs are the documented, company-approved methods for accomplishing every phase of flight and ground operation. They typically cover normal procedures (engine start, taxi, takeoff, cruise, approach, landing, shutdown), abnormal procedures (single-engine operations, pressurization loss, system failures), and emergency procedures (immediate-action items, evacuation). SOPs define not only what to do but who does it, when, and how it is verified.

AC 120-71B emphasizes that effective SOPs must be: clear and unambiguous in language; operationally validated (tested against real flight conditions and simulator scenarios); consistent with aircraft manufacturer's guidance, regulatory requirements under 14 CFR Part 121 or 135, and the operator's Flight Operations Manual; and regularly reviewed and updated as aircraft systems, regulations, or operational experience evolves. The AC also stresses that SOPs should reflect a human factors awareness — they must be written so that a fatigued, stressed, or high-workload crewmember can still execute them accurately.

How Crew Standardization Works

Crew standardization is the process by which all qualified pilots at an operator learn, practice, and demonstrate proficiency with the same SOPs in the same way. This is accomplished through initial and recurrent training programs, line checks, and standardization flights with check airmen who are themselves held to a documented standard. The goal is that a Captain based in Atlanta and a First Officer based in Seattle, flying together for the first time, immediately share a common operational language.

Defined Roles and Callouts

One of the most practical manifestations of standardization is the precise assignment of Pilot Flying (PF) and Pilot Monitoring (PM) (sometimes called Pilot Not Flying) duties. SOPs specify which seat performs which actions during every phase of flight. This role clarity prevents the classic CRM failure mode where both pilots assume the other is handling a task — or, conversely, where both attempt to handle it simultaneously. AC 120-71B specifically highlights that SOPs should define monitoring duties for the PM, including challenge-and-response checklist protocols and deviation callouts such as airspeed, altitude, and configuration alerts.

Checklist Philosophy

AC 120-71B distinguishes between do-list procedures (flow patterns performed from memory) and checklists (verification tools that confirm the do-list was completed correctly). This distinction is operationally critical. Treating a checklist as a do-list — performing each action only when it appears on the checklist — is slower and more error-prone than completing a memory flow and then verifying with the checklist. The AC advocates for a challenge-and-response philosophy for critical checklists, particularly abnormal and emergency items, because it requires both crewmembers to be actively engaged and provides a built-in cross-check.

Sterile Cockpit Rule and SOP Integration

SOPs must be consistent with regulatory requirements such as the sterile cockpit rule under 14 CFR §121.542 (and §135.100 for Part 135 operators), which prohibits nonessential activities and duties during critical phases of flight. Critical phases of flight include all ground operations involving taxi, takeoff, and landing, and all other flight operations conducted below 10,000 feet MSL except cruise flight — meaning flight below 10,000 feet MSL is itself considered a critical phase, not merely a threshold that applies only during certain maneuvers. Well-designed SOPs naturally enforce the sterile cockpit by limiting radio communications, briefings, and non-essential tasks to appropriate phases. Integrating the regulatory requirement into SOP design means crewmembers are less likely to inadvertently violate it.

Why Standardization Matters: The Human Factors Case

Human factors research consistently demonstrates that the majority of aviation accidents involve some breakdown in crew coordination, communication, or decision-making — not mechanical failure. SOPs and standardization are direct countermeasures to the most common cognitive vulnerabilities:

Expectation bias: When crews know what to expect at each phase, they are better positioned to recognize deviations from the norm.
Workload management: By automating the routine, SOPs preserve cognitive bandwidth for non-normal situations that genuinely require active problem-solving.
Fatigue mitigation: A fatigued pilot executing a well-internalized SOP makes fewer errors than one who must think through each step from scratch.
Authority gradient management: Clear SOPs give the First Officer a scripted, authorized basis for speaking up when a Captain deviates — reducing the risk of a junior crewmember remaining silent out of deference.
Skill transfer: Standardization ensures that skills learned in the simulator transfer directly to the line operation, because the procedures are identical.

AC 120-71B explicitly acknowledges that SOPs are the operational expression of an operator's safety culture. An operator that allows captains to routinely deviate from SOPs — even when the deviation appears harmless — erodes the entire standardization framework. The AC warns against normalization of deviance, the gradual acceptance of deviations as acceptable simply because they have not yet caused an accident.

Key Numbers and Rules

10,000 feet MSL: Under 14 CFR §121.542 and §135.100, all flight operations below this altitude (except cruise) are considered a critical phase of flight, along with all ground operations involving taxi, takeoff, and landing.
AC 120-71B: The primary FAA advisory circular governing SOP and checklist development for commercial operators.
14 CFR Part 121 / Part 135: The regulatory framework within which SOPs must operate for air carriers and commuter/on-demand operators respectively.
Challenge-and-response checklists: Required for abnormal and emergency procedures per AC 120-71B guidance; both crewmembers must actively participate.
Recurrent training cycles: Under 14 CFR Part 121, air carriers maintain SOP currency through recurrent training programs whose specific intervals vary by training program type and are established in the operator's approved training program under Subpart N/O.
PF / PM role assignment: Must be explicitly defined in SOPs and transferred with a formal handoff callout when control changes hands.

Common Test Traps

Confusing a do-list with a checklist: The ATP written and oral frequently tests whether candidates understand that checklists are verification tools, not action-initiation tools. Performing actions only as you read each checklist item is slower and less reliable than a flow followed by checklist verification.
Assuming SOPs override manufacturer's emergency procedures: Immediate-action memory items (such as engine fire or rapid decompression) are typically drawn directly from the Aircraft Flight Manual (AFM) and must be accomplished as written; operator SOPs govern the broader procedural framework around them but cannot legally contradict AFM requirements.
Misidentifying the sterile cockpit altitude: The rule applies to critical phases of flight, which include all ground operations involving taxi, takeoff, and landing, and all flight below 10,000 feet MSL except cruise — not simply during takeoff and landing maneuvers themselves.
Thinking standardization stifles CRM: A common misconception is that following SOPs rigidly prevents good CRM. In fact, AC 120-71B and CRM doctrine are complementary: SOPs establish the baseline so that CRM skills can be applied effectively when deviations from normal occur.
Forgetting the PM's active role: Candidates sometimes focus entirely on the PF's duties. The PM's monitoring, callout, and cross-check responsibilities are equally defined by SOPs and are equally testable in ATP oral exams.