Home Why
to Pilots
All  Requirements
By Any Airport
Easy to Buy 'How To' Information & Videos

Map of SA Sites

& Support
FAA AIP  Direct
Easy to Install Easy to Maintain

See Remote Data


Instrument Flight Rules
Commercial Flight Ops (Part 135++) ALTIMETER & VISIBILITY
Ceiling Not Required - Since 1966!
Private Flight Ops (Part 91) ALTIMETER
Visual Flight Rules
Private & Commercial (Part 91 & 135) PILOT'S DISCRETION
"Visibility is the sole criterion to initiate an instrument approach"
click paragraph for PDF of entire letter
Helicopter Emergency Service

Even without any
weather reporting

Revised Operations Specification A021 also permits HEMS instrument flight rules (IFR) operations at landing areas without weather reporting if an approved weather reporting source is located within 15 nautical miles of the landing area or if an area forecast is available.


Forecast of Conditions
Meets Alternate Airport Requirements

An AREA forecast may be used
a TAF is not required




QUESTION: Does a Part 135 operator need weather reporting to determine if a flight is VFR?
ANSWER: A Part 135 pilot is competent to provide weather information for VFR operations.

D.  Part 135. Whenever a part 135 operator is required to use a weather report or forecast for IFR operations, the operator must use weather reports or forecasts prepared by the NWS, or a source approved by the NWS. Where NWS services are not available, the source must be approved by the FAA. If NWS or other approved reports are not available for VFR operations, a pilot in command (PIC) may use weather information based on his own observations or on those of other competent persons. For this purpose, the FAA considers certificated commercial pilots, airline transport pilots, dispatchers, air traffic controllers, and trained weather observers competent to provide weather information for part 135 VFR operations.

Source: http://fsims.faa.gov/PICDetail.aspx?docId=EE2EBFD3E81834CB8525734F007665BC


QUESTION: Is a ceiling required for a Part 135 operator to take off?
ANSWER: Ceiling is only a constraint when the aircraft is unable to maintain the published climb gradient.

2)  Approval of non-federally owned and operated AWOS.

a)   Automated systems installed and operated as independent systems under the guidelines of AC 91‑54 are not approvable for part 121 and part 135 operations. This type of system may be used only as a basic source of weather data for a SAWRS.

b)   AWOS-1 installed, operated, and maintained under the guidelines and specifications in AC 150/5220-16 or part 171 subpart K are not approvable for part 121 /135 operations when operated as an independent system. This type of system may be used as a basic source of weather data for a SAWRS.

c)   AWOS-2 that meet the criteria of AC 150/5220-16 or part 171 subpart K are approved for part 121 and part 135 operations with the following limitations:·   

An IFR operation which requires ceiling information as a condition for conducting that operation is not permitted at airports where AWOS-2 reports are the official source of weather information,·   

AWOS-2 airports cannot be used for alternate airports based solely on AWOS-2 reports (no cloud height information),·

AWOS-2 reports may not be used as the sole basis for determining if VFR conditions exist at airports without operational control zones,·   

POIs must examine each request for approval for AWOS-2 operations and are authorized to impose any additional limitations determined necessary, and·    At airports where ceiling information is required to comply with nonstandard takeoff minimums dictated by part 97 or OpSpecs, IFR takeoffs are prohibited if an AWOS-2 is the sole source of weather information.

Note:   At airports where a climb gradient alternative is specified, however, this restriction would not apply to aircraft capable of meeting climb gradient criteria.

source FAA FSIMS:   http://fsims.faa.gov/PICDetail.aspx?docId=EE2EBFD3E81834CB8525734F007665BC


Our goal has been to selectively obtain FAA certifications and approvals
only when they are of benefit to the pilot

  • Pilots only need approved altimeter to unlock IFR operations, and visibility to unlock commercial flight operations

  • While other weather parameters are useful at times, because they impose no constraint to flight operations their certification is of no benefit to pilots

  • Our sensors for temperature, dewpoint, and wind, like any commercially available sensors, easily exceed FAA and NWS standards,

...But there is nothing to be gained by inviting the bureaucracy any further into anyone's lives than absolutely necessary



Change 3, July 12, 2001
  4-1-9 a, 3. "Many airports are now providing completely automated weather, radio check capability and airport advisory information on an AUTOMATED UNICOM system. These systems offer a variety of features usually selectable by microphone clicks, on the unicom frequency.  Availability of the AUTOMATED UNICOM will be published in the Airport/Facility directory and approach charts."

FAA Weather Requirements      PART 91 (&Fractional)   PART 135   PART 121   PART 97

"...the rule requires a forecast of a specific ceiling and visibility for an airport to be used as an alternate, under 91, 135 or 121. 
Note:  This [requirement] is for use as an alternate, not to meet the requirements to begin an approach.
"An AWOS-AV (altimeter and visibility) satisfies the information required to begin an approach under 135." 

Manager, Commuter, On Demand and Training Center Branch, AFS-250     10-23-06


Ceiling Not Required for Any flight operations



FAA has a new system called FSIMS
Which brings together all the inspector's manuals
Which thus tells operators what they need to do

It makes excellent nighttime reading.


This is a GREAT site - Hooray FAA!

OPSPEC C064, TERMINAL AREA IFR OPERATIONS IN CLASS G AIRSPACE AND AT AIRPORTS WITHOUT AN OPERATING CONTROL TOWER—NONSCHEDULED PASSENGER AND ALL-CARGO OPERATIONS. C064 authorizes an operator to conduct nonscheduled passenger and all-cargo (scheduled and nonscheduled) terminal area IFR operations in Class G airspace or into airports without an operating control tower, with the following limitations and provisions:

A.        Before authorizing C064, the POI must determine that the operator has a method or procedure for obtaining and disseminating necessary operational information. This operational information must include the following:

1)          The airport is served by an authorized IAP (and departure procedure when applicable);
2)          Applicable charts for crewmember use;
3)          Operational weather data from an approved source for control of flight movements and crewmember use;
4)          Status of airport services and facilities at the time of the operation; and
5)          Suitable means for pilots to obtain traffic advisories.
6)          Sources of Traffic and Airport Advisories.

B.        Certificate holders may be authorized to use any two-way radio source of air traffic advisory information listed in the AIM (for operations in U.S. airspace) or equivalent Aeronautical Information Publications (AIP) (for foreign operations).

1)          These sources include common traffic advisory frequencies, UNICOM, MULTICOM, and flight service stations.
2)          In those cases where two sources are listed at the same airport, inspectors must ensure the operator’s manuals have procedures which require pilots to continuously monitor and use the traffic advisory frequency when operating within 10 NM of the airport. The procedures should require communication concerning airport services and facilities to be completed while more than 10 miles from the airport.
3)          At some airports no public use frequencies may be available. In those cases, a certificate holder must arrange for radio communication of essential information including surveillance of local or transient aircraft operations by ground personnel. Ground personnel who operate a company radio for airport status and traffic advisory must be able to view airspace around the airport.

C.        OpSpecs C064 and/or C080 may need to be issued to the certificate holder in order for the OpSpec C081, Special Non 14 CFR Part 97 Instrument Approach or Departure Procedures, to be issued which authorizes the use of special (non-part 97)) instrument approach or departure procedures.

D.      C064 is applicable to part 121, 125, 121/135, and 135 certificate holders. For helicopter authorization, see OpSpec H121. Part 91 subpart K program managers should use MSpec A014 for Class G operations.


!!! See the FAA's Operations Specification 8400.10 CHG 1 !!!


"When turbojets were introduced (1950s), the concept of operating minimums was based on ceiling and visibility"

"The basic turbojet minimums are currently specified as a decision height (DH) of 200 ft. and a visibility of 3/4 statute miles (RVR 4000)."

"These changes were finalized by the publication of U.S. TERPS criteria in 1966. This conceptual change eliminated the ceiling requirement by introducing a decision height (DH) and based landing minimums on runway visual range (RVR) reports, when available, instead of ground or flight visibility reports."

"This conceptual change was necessary because of the limitations in the methods used to observe or measure ceiling and visibility (see section 2, paragraph 495). Often ceiling and visibility observations were taken several miles from the approach end of a runway, and as a result were frequently not representative of the seeing-conditions encountered during the final stages of an approach and landing, especially in rapidly changing or marginal weather conditions."

FAA HQ FLIGHT STANDARDS:  "If the approach minimums require one mile, and a 135 pilot HAS the required visibility, even if they were given a report of 100 foot ceilings, they are authorized to shoot the approach to decision height."

1967 Federal Rule Removing 'ceiling' Requirement: 32 Federal Register 13909



A Very Expensive
High-Maintenance Sensor
of Limited Accuracy

Imposes High Annual Costs
on Airport $$$ to keep functioning

The Problem

with Traditional AWOS Laser Ceilingometers...

Their laser looks at one stationary point in the sky


First, let's clear up the bit of confusion about those often misunderstood numbers on approach plates:  There ARE NO CEILING minimums for civil aircraft, anywhere on an approach plate.





§ 97.3   Symbols and terms used in procedures.

(a) A means alternate airport weather minimum.

(s) S means straight-in landing minimum, a statement of ceiling and visibility, minimum descent altitude and visibility, or decision height and visibility, required for a straight-in landing on a specified runway. The number appearing with the S indicates the runway to which the minimum applies. If a straight-in minimum is not prescribed in the procedure, the circling minimum specified applies to a straight-in landing.

(v) T means takeoff minimum.

(x) Visibility minimum means the minimum visibility specified for approach, or landing, or takeoff, expressed in statute miles, or in feet where RVR is reported.

(e) Ceiling minimum means the minimum ceiling, expressed in feet above the surface of the airport, required for takeoff* or required for designating an airport as an alternate airport.

FAA Part

Takeoff Minimums Alternate (airport) Minimums


P§ 91.175   Takeoff and landing under IFR.
For all other part 91 operations and parts 121, 125, 129, and 135 operations, the flight visibility is less than the visibility prescribed in the standard instrument approach procedure being used.
§ 91.1039   IFR takeoff, approach and landing minimums.
(d) No person may take off an aircraft under IFR from an airport where weather conditions are at or above takeoff minimums but are below authorized IFR landing minimums unless there is an alternate airport within one hour's flying time (at normal cruising speed, in still air) of the airport of departure.
§ 135.217   IFR: Takeoff limitations.
No person may takeoff an aircraft under IFR from an airport where weather conditions are at or above takeoff minimums but are below authorized IFR landing minimums unless there is an alternate airport within 1 hour's flying time (at normal cruising speed, in still air) of the airport of departure.
§ 135.221   IFR: Alternate airport weather minimums.
No person may designate an alternate airport unless the weather reports or forecasts, or any combination of them, indicate that the weather conditions will be at or above authorized alternate airport landing minimums for that airport at the estimated time of arrival.
§ 121.651   Takeoff and landing weather minimums: IFR: All certificate holders.
 ...reports the visibility to be equal to or more than the visibility minimums prescribed for that procedure.
§ 121.625   Alternate airport weather minimums.
No person may list an airport as an alternate airport in the dispatch or flight release unless the appropriate weather reports or forecasts, or any combination thereof, indicate that the weather conditions will be at or above the alternate weather minimums specified in the certificate holder's operations specifications for that airport when the flight arrives.



"For use as an alternate, an airport needs to be forecast a ceiling and visibility which meets the requirements of the regulation or Operation Specification of the particular carrier, either from the TAF or the Area Forecast, or an Enhanced Weather INformation System (EWINS), [or] a carrier's own approved forecast system, if appropriate.  In using any such forecasts, conditional elements are controlling.  The requirement to have a forecast for a particular ceiling in order to list an airport as an alternate has been around since I started flying.... no changes there. 

In any case, when an approach is not capable of being used to support the airport being used as an alternate airport, the procedure shall be appropriately annotated with reverse type "A" NA.  This is done whenever the airport is not served by a full-up weather observation system or when a human observer is not available [no weather available].

Typically, people choose alternates at locations with TAFs and also have the lowest landing minima, since in 91 there is a difference in precision and non-precision alternate minima, and in 135, the landing minima drive the alternate minima (through OpSpecs).  This lets you avoid having Area Forecast "chance of" and "becoming" conditions (which are not as precise as in TAFs due to the area nature of the product) disallow an airport, or have the alternate minima be so high that the airport is unusable as an alternate."

Manager, Commuter, On Demand and Training Center Branch, AFS-250     10-23-06



Alternate takeoff minimums ('A') are used to specify non-standard climb gradients when a standard rate climb will not clear obstructions.  The non-standard climb gradient is specified so that the climbing aircraft will remain separated from the obstructions.

“If an aircraft cannot maintain either standard or the specified alternate climb gradients,
unless the pilot can see the obstructions, they probably shouldn’t take off at all.”


Thus, as a practical matter, if you are a commercial flight departing an airport that is IFR;

AND you can't determine any alternate airport within one hour's flight that is forecast to be above landing minimums, 

AND your visibility is below the minimums for the lowest approach back to the departure airport (example above),

AND you can't meet either the standard or specified non-standard climb gradients (example below), 

THEN you will need  to see-and-avoid the mountains around the airport, if any.