Issue Number 218
August 1997
A Monthly Safety Bulletin from The Office of the NASA Aviation Safety Reporting System
P.O. Box 189, Moffett Field, CA 94035-0189

"Clearance Clarification"

Information found in both written and verbal clearances is frequently subject to misinterpretation. In our first ASRS report, instructions in a published procedure were treated as a clearance by a corporate crew.

The Aeronautical Information Manual (AIM) Section 5-4-1 indicates that "Expect" altitudes are published for planning purposes. "Expect" altitudes are not considered crossing restrictions until verbally issued by ATC.

Another crew fell victim to an apparent readback/hearback error, which resulted in confusion about the clearance, and ultimately, to inadequate separation from another aircraft.

"Reaching" and "leaving" are commonly used ATC terms having different usages. They may be used in clearances involving climbs, descents, turns, or speed changes.


Eye on the Sky

An air taxi pilot credits ATC with a "save" - and his ADF needle with a lesson about weather-induced effects:Automatic Direction Finder Instrument Face Before the advent of on-board weather radar systems, pilots flying near an area of thunderstorm activity would tune their ADFs to a low frequency and watch where the needle pointed. They avoided areas where the needle pointed (indicating thunderstorm-induced static).

ATC also kept an eye on an air carrier crew, who almost followed their ADF needle to the wrong airport.

A cross-check of other available navigational aids might have given the crew contradictory information, motivating them to seek clarification from ATC.


"Shear Luck and Training"

It was "shear" luck that this aircraft didn't roll off the end of the runway.

Windshear can come as a big surprise even when the crew is prepared for it, as an air carrier Captain reports:

The crew's awareness of the windshear and training to counteract it were the keys to a safe outcome in this incident.


Uncontrolled Shouldn't Mean Uncommunicative

Radio communications at uncontrolled airports are sometimes less than optimal in quality and quantity. An air carrier Captain reports that an unclear position report from a tow aircraft at a non-Tower airport almost led to a ground collision. UNICOM operators may not be able to provide all the information an inbound pilot needs, and sometimes may not even have a clear view of the runways. In addition, prudence would suggest that a flight crew discontinue their straight-in approach when faced with soon-to-depart opposite direction traffic.

A report from a general aviation pilot describes how lack of radio communication at an uncontrolled airport led to near-disaster.

One wonders what the helicopter pilot was thinking when crossing the approach end of the runway, as reported. However, pilots should also keep in mind that radios are not required at uncontrolled airports, and that many aircraft are not radio-equipped.


ASRS Recently Issued Alerts On...
False GPWS alert attributed to an altimeter error
SAAB 340B dual engine failure of unknown cause
False FMS alerts following an MD-88 engine failure
G2B pressurization failure due to anti-ice duct malfunction
A320 flight display failure following an Air Data Recorder fault
 June 1997 Report Intake
 Air Carrier Pilots
 General Aviation Pilots