Number 284
May 2003
A Monthly Safety Bulletin from The Office of the NASA Aviation Safety Reporting System
P.O. Box 189, Moffett Field, CA 94035-0189

The Case of the Unstable Approach

FAA Order 8400.10 defines a stabilized approach as "maintaining a aircraft under magnifying glassstablespeed, descent rate, vertical flight path, and configuration during the final stages of an approach." Significant speed and configuration changes during an approach can complicate tasks associated with aircraft control and increase the difficulty of evaluating an approach as it progresses. The evidence presented in these recent ASRS reports demonstrates that instability is no defense when an approach goes bad.

The Hold Up

Air Traffic Controllers play an important role in the stabilized approach concept. Appropriate vectors and traffic sequencing help ensure that approach parameters can be met. But, as this B757 crew pointed out, Controllers also need to be aware of the unique flight characteristics of some aircraft.

Lessons learned: 1) We should have gone around and not accepted the set-up. 2) Approach facilities need to be educated about the capabilities of [various aircraft]. Some can't get down and slow up as quickly as others.... You have to plan ahead. 3) Recognize the importance of a stabilized approach. [Final approach] is not the time to be changing runways, working the FMC, configuring the aircraft, etc.

[We] called Approach Control after landing, voiced [our] concerns about how we were handled...and re-emphasized the importance of a stabilized approach.

The Chase Captain on motorcylce chasing aircraft

Although this Captain did manage to catch up to the aircraft and land without incident, a clean getaway and fresh start might have been a wiser course of action.

The Capture

Without anticipating adjustments required for adverse conditions, a flight crew has little chance of establishing a stabilized approach. This CL-65 crew wisely departed the scene when the alarm went off and managed a more successful glideslope capture the second time around.

The Lockup

A good approach usually leads to a good landing. The student pilot who submitted this report learned that the opposite is also true.

From the instructor's report:

The Escape

This MD80 crew started out with a good approach but had to change their plans when they got hit with a low blow.

From The Maintenance Desk

ASRS receives a number of reports related to aircraft that are damaged during ground maintenance procedures. Many of these incidents involve a failure to activate or deactivate systems in accordance with the sequence prescribed in the appropriate maintenance manual. The maintenance technician who submitted this report did what he was told to do, but someone should have checked that all related systems were set up in accordance the maintenance manual.

When I pushed the Standby Hydraulic circuit breaker in, the pump came on and the leading edge devices came down on the open outboard "C" Ducts (engine cowlings). There was nobody in the cockpit at the time. When someone went up to turn the pump off, they found the Standby Hydraulic switch in the "Armed" position, apparently from the B/C Check the night before. The leading edge lockout pin had already been removed from the valve in the main wheel well.

The engine cowlings and leading edge devices on both sides of a B737-700 were damaged in this incident.

Tail bouncing off aircraftTail End Tales

Although it might seem unlikely that anyone would confuse the MD80/90 tail cone jettison with the aft passenger door/stair operation, two incidents reported to ASRS confirm what Mr. Murphy said, "If it can be done wrong, it will be done wrong."

ASRS Recently Issued Alerts On...
ERJ135 weight and balance incident
Unlit taxiway at a major Western airport
B737-800 loss of F/O flight instuments
MD88 abnormal elevator control response
Questionable baggage weight computations
April 2003 Report Intake
 Air Carrier/Air Taxi Pilots
 General Aviation Pilots